same problem here my daughter is 17 months and am 35 weeks she's uses 2 bottles a day when going to sleep but I want her to stop
My daughter was completely off the bottle by 1 year.
When I weened her off I started giving her sippy cups during the day and one very small bottle at bedtime. After a she adjusted to the sippy cups, I switched to water in the bottles, then a sippy to bed. She took to the change quickly so it wasn't too bad.
Since you have a baby baby though, it might be a little more difficult, just stick to it and try to explain to your son that he's a big kiss now and gets to use the sippy, like it's a huge accomplishment.
My son stopped with his bottle at eleven months and my daughter stopped and just before her first birthday I just started giving them there cups with plain water before they turned eights months and they both did fine with out it once I toke it and if someone offers them bottles they won't drink out of it or will be hard with an 18 month old because I'm sure he is smart and knows the difference
My son is 17mths and still has 1 bottle at night before bed. During the day he uses a sippy cup. He's been using different kinds of sippy cups made for different ages since he was 6mths old. Occassionally now he'll try out of a normal cup but he's still at the age where it's more fun to blow bubbles and end up soaking wet.