Change, I know this is really hard for you. I know it isn't as simple as just making a decision, you have to act on it and that is the scary bit. I do understand.
I answered you with a question just to show there are other options, I think Ive answered already anyway, I said firstly I don't think you could be forced into sending her under those circumstances but I hear you on the proving it part and that is something to look into.
I think it was AF that touched on enabling his alcoholism, what you say about him being sole carer on visits and him being drunk, don't let the thought of that stop you moving forward, it may well be the wake up call to him to get his drinking problem in check. That is his decision though and not one you should feel you are responsible for.
I'll give you an insight to why I am banging on a bit, I know how it feels to be scared of rocking the boat, scared of how things will be after you leave and scared if it is indeed the right thing to do. I was with my EX for about 15 years, I wasn't happy and I knew I/our relationship wasn't his priority, we didn't have the same problems that you are having, but there were good enough reasons for me to leave him.
Probably because my own parents had divorced, I really wanted my family unit to work, I think I hung around longer than I should've because of that. I am aware that that may have hurt my children.
I did leave him and I will not lie and say it was easy, financially it was really hard, He had always provided well for our family while I was a SAHM but I knew before I left that he would be able to dodge paying if he chose to. That was what he did in the end and he hasn't paid a penny towards their upkeep since.
He was angry, he had manipulated me into feeling I didn't have options and I think he played on my insecurities. He threatened me, real serious threats too. He threatened to walk away from the children, then he threatened to go for custody, he also threatened me personally, It was all just words though and because I just called his bluff he didn't go through with any of it.
He has regular contact and is pretty friendly with me nowdays, the first 4 months were the hardest.
So despite all of that and the big changes in circumstances, moving/finance etc, I am so much happier, my boys are happy, their dad is happy and they get to spend time with him without any atmosphere. He has certainly behaved better in the long run than I thought he was going to.
I have thought a few times what if we had stayed together, because I know I could have, but it was fake and I am genuinely happier now.
So I do understand how hard this is.
It could be so much better for you and your family than how it is now.