Hithere
Please do not insult people who is in the spectrum - they do not lack intelligence
This is simple
Do not make comments on the parenting unless requested
If your son and dil dress their kid in cloths you do not like, say nothing
Do not invest insane amounts of money on vacations and expect gratitude when you know you already know you have a bad relationship
Talk to your son you raised and stop giving the evil eye to the dil.
He is adult enough to advocate for himself if he wants to
This is very sensible. It is difficult for anyone to see herself as others see her but trying to do so is often a good thing to do a bit of self examination. Maybe try and look at things through her eyes if you can. If you've already criticised her parenting then that is a hard thing to get beyond, it will be difficult for her to trust you going forward, and remember it's not just what you say that can be a criticism. If things are not harmful, then let it be, As grans, we have had our time as parents making our choices for what we do with our children.
You criticised her and your son for making a big thing about minor things that they are pleased about. It probably comes across as you're not interested in them. What seems a minor thing to you might for whatever reason, be a big thing to them. Does it really matter in the grand scheme of things? It doesn't sound as if you like her, so why do you keep going on holiday with her and the others. What do you get out of it and what do they get out of it, is it what they want? Joint holidays can go very well or they can be a disaster. The times I went away with the in-laws were really difficult, they weren't paying at all, it was meeting up there. They were pretty selfish and only wanted to do what they wanted to do. They could have been happy times but that doesn't work if they behave like that.
Only you can decide what to do with regard to the holidays, some reflection as mentioned above might be worth doing