@oohmavis
me calling my nephew "my little sausage" doesn't mean that I think he's a) mine, or b) a sausage,,,
😂 Made me larf that did!! 
@babybarclay
You have really done yourself no favours here with the mean and spiteful comments about 'only children' ... 'Spoilt,' and 'used to getting her own way' and 'demanding' blah blah blah...
As a few other posters have said, I also know plenty of children/people with siblings who are complete brats; demanding and petulant and sulky and so on, and some 'only' children who are lovely, polite, and courteous. To generalise like this is just nasty.
Plus, some people have ONLY one child as they were unable to have any more, and some people who ARE an 'only' child, would love to have had siblings (even if they are very happy, at some point in their life they would have fantasised about having a sibling...) So comments like yours are just plain unpleasant and unnecessary.
Re your MIL, I agree that YABU, she doesn't mean anything by it, and tbh, you sound a little jealous of the relationship she has with her son/your husband. You also sound jealous and bitter about her 'wealth' and her lifestyle... Alienating a MIL (when your husband gets on with her,) is NEVER a good idea. Neither is making such scathing remarks about her. Do you talk about her like this to your husband?!
I agree with the posters saying there is a lot more to all this, and it sounds like you just don't like her, and anything she does will get under your skin, grate on you, and wind you up.
Maybe you need to start looking into the reasons why this woman makes you angry. As a few posters have said, I can't see that she has done a single thing wrong. And I am willing to bet that she doesn't get 'annoyed' if your husband doesn't call her 3-4 times a week either. I am also willing to bet that he wants to call her.
I also don't believe that 'he moved closer to her so she wouldn't be lonely....' He grew up with her, so if he WAS living near her, surely he was just living in the town he grew up in! 