I.C.
I would suggest a couple changes - between co-sleeping and sleeping in a shared room with his brother, I would suggest an intermediate option: a crib or bassinet in your room, for the nights. You have to train him to sleep there - not with you - but being there in the same room might reassure him - you will respond faster to his cries than if you have to go to the other room. Also you will be less tense when you put him in there, he will wake you up or your husband but not his sibblign. Then I would suggest that you work with naps in the crib in his real room - assuming he still needs a nap when his brother does not.again you have to stay around the room, not necessarily pick him up when he cries, but comfort him with pattings and lulabies and holding his hands. also you have to check with daycare what they do to put him in bed (does he falls alseep on their shoulders? do they pick him up as soon as he cries? are they concerned that he sleeps so short?) I know it is hard, but it is only a habit, so you have (and can) to turn it aournd...
good luck,
isa