Grimm (TV)/Headscratchers

In "Happily Ever Aftermath," why would Lucinda have killed her stepmother?

She had no way of knowing about either the Ponzi scheme or that she refused to help her husband. Also, why is no one suspicious of the stepsisters? Considering that they are their mother's only heirs, they would have the most to gain from her death.

There are various ways for Lucinda to have found out about that without us seeing it. And people did suspect the stepsisters, primarily Lucinda's husband.
True, but they never gave an explanation onscreen, at best it is a Contrived Coincidence
She had good hearing and was snooping around the corner before she appeared on screen when Arthur and Spencer were talking?
- She is a bat after all. Echolocation isn't just about load sounds, its also about good hearing.
News of the Ponzi scheme and the suicide of its mastermind was all over the news. If she knew even a little about her husband's finances, she could figure out that they were financially ruined.

Why hasn't Nick seen Renard's Wesen form yet?

He seems to have no trouble identifying the others.

My guess is that as a Wesen of some high rank, he might be old enough to hide his identity (he might be older than his perceived age), or have some sort of item that prevents the mask from slipping.
So far it seems like Nick can only see wesen if they let the mask slip. Most wesen are like Monroe before he met Nick, and think that Grimms are nothing but a legend, so aren't nearly as careful as they could be. Renard on the other hand seems very much aware of how real Grimms are, and that Nick is one, so it might be that he's just being more careful about it.
We also don't know yet if Renard is a wesen either. He may be more akin to Nick than to Monroe.
It is possible Renard is a wesen that looks human. I always thought he was an elf
Sasha Roiz has confirmed that Renard is not a Wesen.
- So if he isn't a Wesen, what does he have against Grimms that he's involved with the Reapers?
  - Fey/Faerie?
  - He's part of the Royal Families that have some connection to Grimms, the Verrat and Reapers. How it all fits together, we don't know yet. Also, he doesn't seem to have something against Grimms in general.
    - Perhaps he's a Grimm himself? At any rate, being a part of the Royal Families means that historically, Grimms work for him. So he may not really have anything more sinister for Nick other than "Work for me or I give you no protection."

In “Island Of Dreams” Monroe tells Rosalee that he knew her brother, but the first time we see said brother back in “Organ Grinder” It seemed like they didn’t know each other (though Monroe was a least aware of the shop before hand).

It may be that she as implying that he knew him to be a wesen and wanted to know if Monroe was like Nick (a Grimm) or a wesen himself. Know in this case being more akin to 'knowing his true face' rather than know personally. Remember that she'd already seen Nick with Hank and she had commented on the fact that Monroe was a different partner. So she may have been also fishing for information on Nick's relationship with wesen (after all, she assumed he was going to kill her initially just like most). Just a guess though.
- While thats probably true, I wasn't talking about Rosalee. I was talking about the way Monroe seemed to imply he was in someway close to the late Freddie, when from what little we've seen they've had minamum contact and did'nt seem particularly close (or even all that familar with each other).
- Monroe was hitting on her. "I knew your brother" was basically a pickup line. Or at least a way to get her to trust him enough to let him hang around.
- Monroe knew the shop and the protocol. He's probably bought some of the herbal products before, but was not a regular.

Why do all Wesen go by their German species/racial names?

Presumably they don't all originate from Germany or historic Germanic territories. Did the original Grimms coin them and if so why would the Wesen choose to use names given to them by such an adversarial group. If the Grimms didn't come up with the names is German a sort of universally language among the Wesen (none of them seem to use it)?

They don't all go by German names. "Mellifers" is Greek; the bat creatures can be called Spanish "Murciélago" or German "Geölterblitz".
Justified in that the two main characters are both of German decent. Monroe would only know about wesen via German and Nick is both of German descent himself and tends to pick up most of his wesen habits from Monroe (no doubt due to making it easier as well to talk with Monroe about things with a common language). However, both the Grimm book and Monroe make mention of other wesen names in other languages - we've seen spanish, greek, latin, japanese, and a few others mentioned.

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