B.M.
this may sound harsh, but have you tried to ignore him when he starts crying like the other child? maybe if you show him that kind of behavior is NOT rewarded and you are not going to acknowledge it then he may stop. just don't give in because once you do he's not going to stop. and if you make a big scene about him crying all the time he's not going to stop. b/c he is seeing a reaction and that's something to him.
best of luck
B.