Exactly What It Says on the Tin: This is a band trope: Members of a band are related to each other (though it doesn't have to be all of them).

There are two types:

Type 1: Some of the members happen to be related
Type 2: The Family Band: everyone in the band is related—which is quite common.

Common deviations from this formula include

A relative replaces a former band member
Two members are related, but one leaves the band
Two members are married—but divorce

Examples of Band of Relatives include:

Type 1

Film

Jake and Elwood Blues of The Blues Brothers.
- Although Jake & Elwood weren't related by blood, they were Blood Brothers.

Real Life

Van Halen. Which included the brothers Eddie and Alex Van Halen, Eddie's son Wolfgang, and a few others (currently David Lee Roth).
Oasis: Noel and Liam Gallagher are brothers—and brotherly love is nowhere to be found.
The Statler Brothers: None of them were named Statler, but Don and Harold Reid are indeed brothers.
The Beach Boys had the three Wilson brothers (Brian, Carl, and Dennis) and their cousin Mike Love playing in the band.
Andy Creeggan -- The Pete Best of Barenaked Ladies—is the brother of bassist Jim Creeggan. They have a side project known as The Brothers Creeggan.
No Doubt had Gwen Stefani and her brother Eric.
Led Zeppelin: The band split after John Bonham died. During the 2007 reunion, Jason Bonham (John's son) took his father's spot.
ABBA were two married couples. The couples divorced, and the group disintegrated.
Good Charlotte has twins Benji and Joel Madden.
My Chemical Romance has Mikey and Gerard Way.
Arcade Fire has Win Butler and Regine Chassagne, who are married, as well as Win's brother Will.
ACDC: Malcolm, Angus, George, and Stevie Young. The first two are well-known. As for the other two?
- George (brother of Malcom and Angus) was the bassist for a short period of time.
- Stevie Young (the son of Malcom, Angus, and George's brother Alex) filled in while Malcom dealt with alcohol dependancy (because they looked so alike, not many fans were aware there was a switch).
The Mamas and the Papas included husband and wife John and Michelle Phillips.
- Their daughter's band Wilson Phillips is also an example, but not because of Chynna Phillips. Carnie and Wendy Wilson are sisters.
Eisley is the Dupree sisters, plus their cousin and a friend.
Five Iron Frenzy: Micah Ortega and Leanor Ortega are cousins.
New Kids on the Block very briefly had two brother pairs: Aside from Jordan and Jonathan Knight, Mark Wahlberg was in it for about 5 minutes along with brother Donnie.
The Jesus and Mary Chain: Jim and William Reid, the band's two constant members, are brothers. Later, they went on to be heavily involved in . . . .
Sister Vanilla: A group which features their little sister, Linda, and occasionally the brothers themselves.
Paul McCartney and Linda were in Wings.
John Lennon and Yoko Ono were in The Plastic Ono Band. And so, at one point, was Sean Lennon.
bôa, the British rock band best known for providing the theme song for Serial Experiments Lain, has Steve and Jasmine Rodgers, who are brother and sister.
Dixie Chicks: sisters Emily Robison and Martie Maguire; they've also recorded as a type 2 duo, the Court Yard Hounds.
Alabama: cousins Randy Owen and Teddy Gentry.
Heart: sisters Ann and Nancy Wilson.
The Kinks: Ray and Dave Davies. They did not get along well.
Ace of Base: Jonas Berggren was the brother of Malin "Linn" Berggren and Jenny Berggren. Subverted now that he's the last Berggren in the band.
Radiohead: Colin and Jonny Greenwood (bass and lead guitar, respectively) are brothers.
Spacehog's Royston and Antony Langdon are brothers.
The Black Crowes have brothers Chris and Rich Robinson. In 2001, The Black Crowes actually toured with the already mentioned Oasis and Spacehog, in what was known as The Tour of Brotherly Love. The tour name was meant to be ironic, as all three sets of brothers weren't exactly known to get along.
Briefly, The Flaming Lips: Their original lineup had Wayne Coyne on guitar and his brother Mark on vocals. Mark Coyne left the band after their first EP, so Wayne took over singing duties.
INXS has lead guitarist Tim Farriss, keyboardist Andrew Farriss and drummer Jon Farriss. In fact, the band's original name was the Farriss Brothers. Many don't know this, probably because Michael Hutchence wasn't one of them.
The Wu Tang Clan:
- RZA, GZA & ODB - Cousins
- Method Man & Raekwon - Cousins
  - The familial connections expand for more cousins, children, siblings and adopted relatives with the second and third generation Wu members and affiliates.
The Allman Brothers Band featured Gregg (keyboards) and Duane (guitar) Allman along with non-relatives, but the band name became an Artifact Title after Duane died in a motorcycle accident in 1971. In fact, since they had their greatest success after Duane's death, he almost qualifies as a Pete Best if he wasn't their most famous member.
Creedence Clearwater Revival, with brothers John and Tom Fogerty.
Danielson Famile consists of Daniel Smith, his brothers and sisters, and some friends (including Sufjan Stevens) who are close enough they may as well be family, too.
Devo had two sets of brothers at one point - two Casale brothers and three Mothersbaughs. Currently, it's two of each.
The eight members of Los Campesinos all share the pseudonymous last name "Campesinos" but only lead singer/songwriter Gareth and keyboardist/flautist Kim are related - they're brother and sister.
- Kim and Gareth also count as a subversion: Kim replaced the band's original lead female singer, Aleksandra, in late 2009.
Veruca Salt's initial lineup included Nina Gordon on guitar and her brother Jim Shapiro on drums.
The band Meg and Dia was founded by sisters Meg and Dia Frampton.
The Meat Puppets' Curt and Cris Kirkwood. Curt pulled an I Am the Band for a few years without his brother (or original drummer Derrick Bostrom), but from 2006 on both brothers have been in the band again.
B*Witched's twin sisters Edele and Keavy, until the group's breakup. See below for their current act.
Brazilian band Capital Inicial has Fê and Flávio Lemos.
Mexican band Maná started with three brothers in the group, Juan, Ulises and Abraham Calleros. The first is still a member, and the second is the band manager.
The original lineup of Jellyfish included brothers Roger (keyboards/backing vocals) and Chris (bass, backing vocals) Manning. However, Chris only joined after their debut Bellybutton was recorded, though he appears on the album artwork and is credited as "band witchdoctor and mime".
Jaga Jazzist: Siblings Lars, Martin, and Line Horntveth are almost the only musicians who have been with the band for its entire existence.
Jagged Edge has twin brothers Brandon and Brian Casey along with Kyle Norman and Richard Wingo.
Sepultura had Max and Igor Cavalera, who later reunited in Cavalera Conspiracy.

Type 2

Live Action TV

The Partridge Family. A mother, three sons and two daughters.
Arrested Development: Dr. Funke's 100% Natural Good-Time Family Band Solution, which consists of Tobias, Lindsay and Maeby Funke. One public performance ended up being given by Tobias, George Michael, and GOB's wife.
On The Brady Bunch the Brady kids became The Silver Platters in order to win enough money to pay for their parents' anniversary gift of an engraved silver platter.
- Defictionalized with the Brady Kids, where the six (unrelated) actors went on tour as a "family" of six singing Bradys.
- And then there was The Brady Bunch Variety Hour, where Mike quit being an architecture so he and his family could host a Variety Show.

Film

Disney's The One and Only, Genuine, Original Family Band. 10 people altogether: grandfather, mother, 5 daughters and 3 sons, each with a different instrument.

Western Animation

The Brady Kids
The Griffin family briefly became a musical act on Family Guy

Real Life

The Jackson Five. All siblings.
The Cowsills, the inspiration for The Partridge Family. The mother, five brothers and a daughter.
The five Osmond Brothers (after 1971).
Sons Of Sylvia consists of 3 brothers.
The Band Perry has a sister and her two younger brothers, all with the last name Perry.
The Corrs
Hanson: All three members are brothers.
The Bee Gees for the majority of their history have consisted of three brothers: twins Robin and Maurice Gibb and older brother Barry.
Irish folk/NewAge group Clannad. The members included the Brennan siblings (Moya, Pol, and Ciaran) and their twin uncles (Padraig and Noel). Another Brennan sister, Eithne, joined briefly before becoming known as solo star Enya.
The Shaggs were a band of three (later four) sisters: Dorothy, Helen, Betty, and Rachel Wiggin . Their father insisted.
The White Stripes—at first thought to be brother and sister, it turned out to be husband and wife. Subverted when they divorced, but kept going for around another decade.
The Trapp Family Singers: Maria von Trapp, her husband Georg Ludwig von Trapp, and her stepchildren (also her and Georg's own children when they became old enough).
The Everly Brothers.
The Ronnettes consisted of two sisters and their cousin.
Disney's The Jonas Brothers.
The Carpenters.
The founding members of Thrash Metal band Death Angel were all cousins.
The Court Yard Hounds, as mentioned above.
Kings Of Leon is made up of three brothers and their cousin.
Nelson is twin brothers Matthew and Gunnar.
The Staple Singers were Roebuck "Pops" Staples, joined by daughters Mavis and Cleotha and son Pervis. Pervis left and was replaced by another Staples offspring, daughter Yvonne.
The Free Design - two brothers and three sisters.
The Gregory Brothers, consisting of brothers Evan, Michael and Andrew Gregory, and Evan's wife Sarah.
The Trachtenberg Family Slideshow Players are a husband and wife, with their teenage daughter on drums.
The members of the Australian pop duo The Veronicas are twin sisters.
MsLynch consisted entirely of the former B*Witched twins Edele and Keavy. Then they dropped the act and formed another one, Barbarellas.
The members of indie rock band Smoosh (Ayse, Maia, and Chloe) are all sisters.
Mates of State are a husband and wife duo.
The Nolan Sisters, an Irish singing family who were big in the late 1970's and 1980's. They are curently riven by dissension of various kinds and brandishing lawyers at each other. Youngest sister Colleen is probably the most successful, as she has permanent tenure on talk show Loose Women. The sisters apparently remain Big in Japan.
LMFAO—an uncle and nephew duo.
For their first three albums, hard rock band Chevelle consisted of brothers Pete, Sam and Joe Loeffler. Joe left the band in 2005, and was replaced by the brothers' brother-in-law, Dean Bernardini.
Indie rockers The Cribs consist of brothers Gary, Ryan and Ross Jarman, except for a period between 2008 and 2011 when Johnny Marr was also a member of the band.