I agree with you Lolo the OP hasn't been rude or behaved badly which is to her credit but there's an underlying 'theme' throughout this thread that bothers me.
Suggestions have been made that when her H visits his parents at their home that she doesn't go, but she appears unwilling for him to take their child with them. This would greatly reduce the amount of time she would spend with them, as she'd only see them in her own home.
More than once the OP has commented on the close relationship her H has with his parents and I wonder if her resentment of that relationship is a source of annoyance to her.
What struck me was that despite the last visit going much better, with the OP's H being "super aware and caught it (their rudeness) several times" at the end of her last post she says "He's talked of distancing himself. I don't know what the right answer is I'll just keep supporting him".
Why is her H thinking of distancing himself? Could it be that disregarding the conversation they probably had before his parents arrived, where they discussed their 'strategy', and the inevitable conversation once they'd left about the positive and negative aspects of the visit, this is a constantly referred too issue, and it is that and not just his parents behaviour that is affecting her H?
The OP told her H she loves him more than anything and if he needs her too she'll "just fake it for him". That's a terrible burden to put on the man you love more than anything isn't it? That you're so hurt and upset by the way his parents behave toward you, that because you love him so much, you'll grin and bear it for his sake.
Then there's the reference to letting them "hold DS and let them take pictures with him". I agree with Madgran here, it sounds as if the OP doesn't want her in law's holding their GC and taking pictures; if that's the case then why?
I understand her resentment and frustration because of a very difficult relationship for several years with my own m.i.l. but that had nothing to do with her relationship with our boys, and shouldn't have anything to do with her in law's relationship with their GS.
The last visit appeared to go much better than previous visits and yet there's a sense that this isn't enough, so what's the answer?
The OP can only see her in law's in her own home with her H visiting his parents with his son, thus reducing perhaps by as much as 50% the number of unpleasant and uncomfortable visits for her to be a part of.
If she doesn't want her in law's seeing their GC without her being there, although I really don't understand why, she and her H can continue to work together to make visits as bearable as possible.
Her H can distance himself from his parents, which I seem to remember he did for several weeks before contact resumed, but what effect would/could that have on him if this went on for a protracted period?
If he feels that he must choose, as Nell put so well he will in all probability choose his wife over his parents but she'll "lose a bit of him along the way".