popcorn, I can see that you are trying extremely hard to keep things amicable for the kids here. However, you need to accept that your XH is an abusive man and that slightly different rules apply.
The biggest thing you need to do is accept that you cannot avoid a confrontation with him if you are really going to start laying down effective boundaries. He is an abusive man and he will show off once you start standing up to him. So unless you are prepared to be bullied by him for the rest of your life, you need to accept that you are going to have at least one unpleasant conversation if you are to move forward. FWIW, I also left an abusive partner who didn't accept the break up. Thigs were truly awful when I first left. However, within 4 months of my leaving and setting new boundaries, he totally capitulated. Now I have no bother and we get along really well. I was always friendly, but as soon as he behaved unacceptably or inappropriately I made him leave. No discussion. Took less time than I thought before the message sunk in.
I am appalled that he is making you kiss him each time you see him. The staying in the same bed idea is very, very, very bad. Things could get out of hand, and I guarantee that if it did, he would blame you by saying you gave him mixed signals by allowing him to share your bed.
You owe him NOTHING apart from the opportunity to be a part of your DC's life. Inviting him over early in the morning to see the DC open their presents and inviting him for lunch is generous enough. He is not entitled to anything further, no matter how much he insists he is.
If he protests and refuses to come over, that's his loss. If he comes over and refuses to leave, can you call someone to come over and 'persuade' him to leave? If he kicks up a fuss, it will be his own image he is tarnishing to your DC, not yours. Ultimately, your DC need to see you stand up to him more than they need to see you be walked all over by him in a caring, but misguided, attempt to keep the peace.
Is your XH on email? If you have qualms about dealing with all of this, one way you can start the ball rolling is to email him. You can tell him what you have decided for Christmas and that it is not open for negotiation. Keep it friendly and polite (remembering that anything you put in writing may be used against you) but be very, very firm. Then you can move on to the fact that you want him to stop kissing you when you meet because it is inappropriate and sends confusing signals to the DC. Emailing is a way of getting your point across without running the risk of being browbeaten by him in person. It also gives him a chance to calm down and digest what you've said before he sees you. Furthermore, if you are careful about what you right, should things get ugly and go to court, you will have written proof that his behaviour has been going on for some time and that you have behaved in a restrained and reasonable manner in an attempt to deal with it.
Decide in advance what you will do if he breaks these boundaries, and stick to your decision. No matter what he says, do not allow him to convince you that if you really cared about the kids you would allow him to do this that and the other. That's manipulation and your kids will benefit far more from seeing you refuse to bow to it.
One of the best ways you can move forward is to keep contact purely as contact, rather than as a means of helping you out. I know this is easier said than done, as childcare can be difficult, but it will give him far less control over your situation and make his relationship with you more about the kids and less about control of you.
I really feel for you. What a time of year to be facing this. I know you will be worried about Christmas Day and him causing a scene, and I wouldn't judge you if you decided to just 'let it go' for this year as you don't want to spoil anyone's Christmas. However, please consider you and your DC worth standing up for sometime very soon.
Best wishes.