i've started am earlier thread on waking at night so can't give you any major solutions. However, it always seems easier when it's not your own problem - so here goes, at least you know someone has read your notes!
It really sounds like he has separation anxiety quite badly. I have read that they can get this when they go to sleep. Maybe your daughter wasn't as bad - so it's more of a shock. Given his health history it was unlikely that he was going to get into a good routine early on (you didn't have a chance from the sounds of it")
They do say whatever you do you must be consistent. Maybe sometimes giving him a bottle, sometimes sleeping with you has confused him?
Agree your strategy with your husband and stick to it. If he is only having 2oz then he really does not need to eat during the night. Can you get your husband to see to him if he wakes up?
Also sounds like you are rushing in quite early because of your little girl, which could mean that he is rewarded with mums attention at night he cries or makes a fuss. Think about what you do to help him settle back down, eye contact, maybe a feed, talking to soothe him, picking him up, rocking etc, using any props?
Take one problem at a time, first get him off the milk feeds either by giving him cool boiled water when he wakes instead of milk then phase that out, then maybe the props...
I am afraid though that almost all the books i've read say at this age be prepared for some tears, even softy approaches.
I am sure it hasn't helped, but rest assured I really do sympathise, there is nothing quite like sleep deprevation