Allen's peeing right now, and I KNOW its behavioral since he's been checked out. He is ticked off the room he used to call his own is now being occupied by my son who's home from college. He pees on blankets and in laundry baskets right now to show his disapproval of HIS room being taken over. I know this because it doesn't happen when my son is out of the house, only when he's here, especially when he's in "Allen's" room.

They could also be upset that one of them is gone. Cats are very sensitive to change and each one handles change differently.