hi there. just had to stop in a give a plug for the other side.... i'm all for letting babies keep their bottles until they are older. my two girls each kept a bottle until they were 2 1/2. just at naptime and bedtimes and i think they might have had one in the middle of the night at least until right around the time they turned 2. we never had to do anything to wean them off the night bottle, they just all of a sudden started sleeping through it.
when my girls turned 2 1/2 i took them to the store and let them pick out a special cup just for milk.... i remember my first was a huge dora fan at the time, so she got a pack of dora cups and from that day it was "dora milk" and she never asked for a bottle again. with my second, she picked a pack of gerber cups that had frogs on one and flowers on the other and so she had "froggy milk" and "flower milk." she wasn't as easily swayed by the cups, but she used them.... grudgingly at times, but she used them!
my girls are 3 and 5 now and their teeth are perfect. never had any cavities, stains, decay, weird shapes..... just perfect pretty healthy teeth. and they sleep wonderfully through the night and they are just really good healthy happy kids!
i think if you make sure to remove the bottle from your little one's bed after he's asleep and make sure to brush his teeth daily, then he'll be just fine. given that your son is 16 months old, and he's trying to get used to sharing the spotlight with a new sibling, allowing him to stay in his current routine is really the best thing you can do for him.
anyway, hope this helps a bit!