I don't know how common of a sibling experience it is, but there's a fun thing I used to do with my sibling where one of us played a game while the other backseats. When the one playing fails/loses/dies/etc. , we would swap places.
Could make for some fun interactions between the twins if they did this.
ex. of potential interaction:
"You can make that jump"
[Jumps and dies] "You were wrong."
"lmao get jebaited"
[They swap]
[Proceeds to do the same thing and dies]
(credit to jeiysoo and koutaking in NN for the example)