Throw the bottles away. Perhaps have a ceremony during which he passes the bottles on to babies who need them. If there are no bottles there is no issue. He'll get used to drinking milk out of a sippy cup. He may refuse at first. Accept his refusal and keep giving him a sippy cup with milk. Stop putting energy into the issue.
Is it possible that the tension between yourself and your husband is adding to your son's insistence to drink milk only from a bottle? Are the two of you able to work together on getting rid of the bottles? Find a way to let go of yur irritation with your husband.
My grandkids made the switch at night from a bottle of milk to a bottle of water and from a bottle of water to a sippy cup of water. By the time they were 2 or so they took a sippy cup of water to bed with them because they would be thirsty after they got into bed. This eliminated the one more drink of water request. I noticed that they sometimes picked up the sippy cup during the night and took a few sips. I think this helped them stay asleep or get back to sleep. Perhaps I understand this because I keep water on my bedside table and sometimes wake up thristy.
I suggest getting rid of the bottles and give him milk in a sippy cup. Give him water in a sippy cup when he goes to bed. It may help to include him in getting rid of the bottles. You can do it over a few days time by saying that in 3 days the bottles are going away because he's a big boy. Or you can have him help gather up the bottles, put them in a gift bag, and talk about giving the bottles to little babies who need them and how he's a big boy now and can use his sippy cup.
He may protest. That's OK. You are asking him to make a big change. It's normal to want to stay the same. However, changing is going to happen to him all of his life. You do not want to protect him from change. You want to help him learn how to deal with change. It's important to let him express his feelings without judgment while encouraging him towards success with the new way of doing this.