I don't play splatoon so I have 0 familiarity with the character designs, but it looks like the arms on the purple one are attached a bit too low. The shoulder is basically missing, if you moved the arm a bit up and turned the top line into one line (instead of the v-shape it is now) it would look ok. On the green one the boobs (is that what they are? That bulgy part of the chest) come up a bit too high and it looks like there just isn't an armpit anywhere.
I have no experience. I have know knowledge on playing Splatoon, in terms of the story and characters, and experience. I'm saying that your poses are getting to be on the right track.
I think, that if I was to give you a suggestion to improve those bodies of arms of either sister character, then it would be to really and totally make to Left girl more timider, while you make the older sister much more bolder as far as the lines of action and balance are concerned; all warming up to 42 minutes of 30 seconds of Nintendo and Splatoon poses, all working more loosely and confidently, would you please do those?
The reason is because, your acting and posing choices will become even most stronger in terms of the vitality and humor. Ooh, and one more thing, would you like to please add a brighter, but not to bright pink highlight on one of the sister's tentacles. So, it'll make the values and colors more perfectly readable.
Hope they have been completely and totally a pivotal and vital asset. Happy cartooning!