If I might interject, Ryu and Ken from Street Fighter makes perfect sense at the name as is, to be fair. They started out nigh identical save a minor change in clothing and while they have diverged somewhat over time, they retain mostly identical movesets, though each has their own unique skills and specialties regarding the moveset that still act as a small but crucial distinction.
The trope in is about two characters joined at the hip for some narrative reason that while largely similar, still have crucial differences, specifically regarding abilities. With this in mind, "Two Characters, One Powerset" by @Robkelk is not entirely bad either.
That all said, the key difference is while they may have the same powerset, it's how they best utilize it that is the defining factor.
Typically, as Street Fighter has progressed, Ryu has tended more towards being more specialized in use of his fireballs and spinning tornado kick. While Ken has the same moves, he more focused on improvement to his Shoryuken (jumping uppercut). Both trained under the same master and have access to same base abilities, but each has specialized into a key niche within said powerset.
Therefore, a slightly more precise name for identifying this key distinction between two characters would be ideal. So if we MUST rename the trope, a somewhat more precise version of Rob's suggestion would be best IMO.
Now, while not strictly relevant to the discussion, Sakura (Ryu's fangirl) was brought up, and while she falls outside the trope definition for many reasons, her abilities are best described as "a reasonably good while still quite different approximation" of Ryu's skills. Specifically, while her skills follow the base forms of Ryu and Ken's base moveset, her fireballs are totally different (hers have less range as the grow in power, Ryu and Ken have no range limit), her Shoryuken is quite different (the timing, range, and hitboxes are quite different), and her spinning kicks are best described as a degraded form of Ryu and Ken's own versions of the same.
That said, she's more of a "Shotoclone" due to how much her abilities were developed independently and how despite basing them off Ryu's they work in practice much differently.