My advice to you, having had a 12-year-old who refused to go to contact which meant I was in breach of a court order..
if he comes to the house when you’ve told him not to you are within your rights to call the police because this is harassment. If I was you, I would start by speaking with the police and find out whether they think you should seek a non-molestation order. They may also be willing to have a word with him and tell him to stay away and that if he wants to pursue this, he will have to go via the courts. That is what he will be told if he seeks advice on this from anyone, I think, so it’s kind of inevitable that it will go on his radar at some point if it isn’t already. The police can help you if there is a breach of the peace, they can come to your house and remove him if he’s refusing to leave your front door for example
if the kids have already told him they don’t want to see him, I would not put him in the position of having to do this again unless they want to.
in terms of a court order, the courts can’t make her go, they might give you a hard time about it, but ultimately all they could do is actually change residence and as frightening a prospect as that is, I don’t think you need to be worried about it. The longer it takes for it to go to court the more weight the courts would give to her wishes and feelings, she certainly rapidly approaching an age where they would say you can’t be expected to force her. I think you’re alright, but if he does take it to court, you might find you have a bit of a bumpy ride. I don’t think you’ve got much choice though. The fact that he hasn’t applied for one already is positive, for you to have got this far through child rearing, maybe he won’t do it.
if I was you, I would shield you kids as much as possible (don’t make them talk to him, don’t allow him to come to your house,), take the pressure off them as much as you can, and then in the background do everything you can to show you are working with dad so if he does make an application you are in a good position. You could request that he works with you and a highly qualified family therapist (eg ddp or similar) so that you can become better co-parents and reduce parental triangulation so that you can help the kids feel better. He will refuse of course. you could also approach anyone you think might be able to help work with your daughter who has had a horrible experience, even if she doesn’t want to take up the offer it will show that you take what’s happened to her seriously, and have sought support. If you can’t afford these things, you might be able to find some free resources that are equivalent
I’ve been through a decade of absolute hell in the family courts and I know how awful it can be sometimes but I do think you will be okay. If he does make an application feel free to PM me because I could advise further on some good resources
Good luck x