When the parents said they put them back together in the same room did they mean in separate cribs or back into the same crib. It is common for twins to often sleep in the same crib - one at each end or at least starting out that way because they are so used to being together. Can you make sure he is snuggled a bit more as in a blanket swaddled around the middle of him so it feels like something(one) is near him.

If it is just the two of them in the room and the brother is fine with the tears then I would just leave him.