Everything @saraclara said.
They asked me to their house a couple of times in the past, saying that they would like to go for dinner. And then my mother in law spontaneously invited my husbands ex- wife “It would be nice if you get to know each other”
At which point I would have said "Ooh, lovely, yes, I'd love to go for dinner and for us to get to know each other better, but at the moment, I'm not ready to start a relationship with {insert name}, so let's keep it just the four of us this time. Now, when are you free?"
The whole present thing is not what you need to focus on. I genuinely can't see what they are supposed to have done wrong here. I would assume a present from my ds and DiL was just that - a present from the two of them. They thanked the one half of the couple that was there. The one that was willing to actually meet with them,and he shared that thanks with you when he got home. I would not expect them to then separately contact you even without you being so unfriendly to thank you separately.
I think you’re being awkward and aloof and that’s fine - you don’t have to be friends with anyone, you have a perfect right to hate them all but just own it. Don’t try to justify it and make out that they’re bad people for wanting family unity. You are part of a blended family after all, whether you like it not.
The more I think about it, I can't believe that in 3 years of marriage (and presumably all the preparation for the wedding beforehand, even if not in the 'going out years' before the proposal) you've not suggested having them over for a meal, or going out for a meal, or invited them to something you are doing they might enjoy, or spending time together in any way. It is just bizarre. (By 'you', I mean 'you' as a couple, not solely you as an individual).