💐. You must be exhausted.
If I were you I'd have a stiff drink or 3 post on the SN board.
There are a few different SN's that he seems to have traits of, possibly he has several or possibly you need to narrow it down more.
It's not going to help at all to treat him like a rude, obnoxious, little shit of the NT variety if he's not. Of course having a SN doesn't give him a 'free pass' - any one with any sense knows that, but they also know that he needs strategies to cope that are more socially acceptable. He wanted out of the busy, noisy, restaurant as he was over loaded, he did/said what he thought would get him out of there, what he needs is to be taught the specific skill for that - not to be told off for not automatically knowing it. Same with the iPad, right now it's his way of 'get no away from it all'. He felt he needed it, not just wanted to play on it like an NT 7 yo. It doesn't mean he can always have the t & he certainly needs to ask more politely, but he needs to be taught exactly what that is.
He comes across as a rude, obnoxious, frustrating little shit who needs telling, but actually, he's a little 7 year totally not coping 😢
Good luck to both of you.
Oh & re the MIL, if you don't want to go NC (which I probably would) then I'd limit her visits to when DS is at school. You're unlikely to change her attitude, somsave your energy & do damage limitation instead.