M.B.
We have basically the same split in age for my youngest 2 (boy/girl). We had the boy (older one) go to a twin bed and then converted the toddler bed back to a crib. He sleeps along one wall and she sleeps along a shorter wall. They are now older 5 & 3 and he is still in his twin bed and she is in the (crib converted back) toddler bed now. We don't have the extra space to let each one have their own room but we know that we can only have them room together for only so long. So we need to think of a new solution within the next year to year & 1/2. By age 7 of the boy, they should be split--but that is just my opinion.
Good luck!