Unborn twins and last name debate.

So me and my ex broke up when I was 20 weeks pregnant. I had agreed to give them his last name cause I thought we were going to be together. Well, I went back on my word. But during the break up I was in the hospital for depression and I mentioned options of him having full custody or adoption because I was still in love with him and didn't see how I was going to raise them. I also mentioned I wanted to them to have my last name since he wasn't willing to work it out with me. I have gotten myself better and he swears up and down he told me he wanted them full time and I said no, that was a lie and I didn't mean what I said. I told him that that was true, but not about the last name thing. I couldn't give up my children. I want them in my house. I remember differently and I remember him agreeing to joint custody. I also already have a daughter with my last name.

What a mess!

Anyway, he and his mom are super upset about it. I can't stop thinking about it. I want to please him and the family, but he hasn't been there for me during this whole pregnancy. He came to one appointment since the break up and two sonograms in the last month. He just recently started to come around to help out a bit and I feel he wants praise for the little effort he put forth.

Was also thinking we could hifen the last name?? I don't know what to do!

Any help or insight?