My kids are only 2.5, and although they play together they also like different things, but they are boy/girl so that helps. It's mroe common with same-sex twins for them have similar interests, just like many same-age, same-sex children would, related or not.
I had read somewhere (can't remember) about whether to seperate kids for pre-shool (not at age 2, for older kids like yours) or kindergarten, and basically what the person said was that if they CAN make friends seperately and CAN function ok without each other there then leaving them together is fine. But if they are overly dependent on each other, or one or both do not interact well with other children and can't play well with them, then you should consider seperation so they can have the opportunity to learn how to do those things.
Hope that helped a little
.