Congrats on Baby #2. I will keep baby 1 where he or she is now and not move him or her. Little kids needs stability and do not like change, especially now that a baby is coming. I would put the second crib in the guess room for now. You will have the baby with you the first few months, so have guess sleep there, When you are ready to move baby to his or her new room, move guest to basement or rec room. Babies take priority over guests in my mind. You want your kids sleeping :)
That is just my opinion. You can also have the kids share, but since you had sleeping issues, I will wait on the matter until the kids grow up a bit.