Two kids, one room

I have a 3 year old and a 4 month old. Our house is small so both our kiddos have to sleep in the same time. Until now the baby has been in a bassinet in our room but he is starting to get too big and will have to transition to the crib soon. The crib is too big for our room so he will have to be in his brothers room. I am not sure if I should put the baby down first or my older boy, I feel like putting them down together might be really hard. Has anyone out there had any experience with this situation? Any advice is appreciated.