Why do you think he is saying this?
Does he see how it is affecting the child?
Do you have family you can ask to help?
Why do you think he started this?
I can't be positive but it sounds like he is having some type of breakdown. Sometimes fathers will look at the stepchild as a threat to the "real" child that you have "together". He's already shown that he doesn't care how this affects your daughter and he is in fact already causing mental and emotional damage to the child. If this continues, she could end up with some serious problems, if not already. This will also affect the other children as well. You are very right, you shouldn't have to convince him that you love your son, and he should not be forcing you to prove this is any way. I can only imagine how this is making you feel, and I really want you to see the danger in what's going on here. You have to think about more than yourself right now, if he were to hurt or kill you, who would have custody of her? He probably would if he didn't get caught and who knows how he would treat her? The next time he hits you, he could kill you. I know you said that you have no where to go but there are shelters who will help, organizations that will protect you. He may be experiencing some type of illness or breakdown that is causing him to act this way, but if he won't get seen, then he needs to go to jail, either way you can be safe. The kids can be safe. But he has to get help someway to figure out why he's behaving so irrationally.
I welcome your thoughts, let me know if you want to talk more.
You're very welcome. You've been on my mind a lot and I hope that you take care of yourself and your babies. There's something wrong with him right now, and whether it's temporary or permanant remains to be seen, but not at the cost of your life or the well being of your kids. Feel free to request me by name anytime you want to talk. Please take care, and drop me a line sometime and let me know how you're doing.