Your post makes me sad and mad in equal measure. You say that his 3 children AND their spouses don't respect you both.
Yet, after all this time, and the fact that they may be his 'children' but are middle-aged adults and should have lives, Christmases and all the attendant preparations for that, of their own, he clearly doesn't see that their destructive behaviour still has him where they want him. They may even be keeping in touch whilst treating him so badly only because they wouldn't want to miss out on an inheritance in future. He's allowed them to disrespect him for the longest of times and you have suffered accordingly. Extraordinary. Surely you are both worth much more than that.
Why would you, either of you, wish to still be involved with a very bitter ex-Wife - and 3 offspring who have never been taught how to behave and who clearly have lots of growing up still to do, to the extent that Christmastime, which you love, is spoiled?
Your DH made his choice a long time ago, the marriage ended, he married you, he clearly has tried very hard to make life as comfortable as possible for the parties involved, but there seems to be some entertainment still to be had in bad-mouthing you and him and showing contempt for all your efforts and who you are. Why on earth is he wasting a moment and enabling such bad behaviour?
If your DH can't see all the harm and leave them to their own devices - especially at Christmas, and plan your own arrangements, maybe just sending presents, for which you will possibly not be thanked - then why not have your own Christmas together or with friends or other relatives and suggest that if he wants to see them, he alone can arrange to see them for a meal out somewhere, but pre-Christmas or New Year, or just for a drink. If he loves you, he should understand that enough is enough and his weakness and tolerance of bad behaviour for so long should not be impacting on you when you tell him that you're not tolerating it any longer.
They've had their 'fun', In your position, I'd be putting down my foot very firmly now and ensuring that our lives came first, our arrangements and friends and interests took priority over anything else. Nothing to lose and everything to gain.