Thank you Rebel and Jgnat,
I now WON'T be going to study with her, I WILL openly invite his siblings in for a coffee, when they have walked past my stables or house for the 3rd time. MIL is mostly sending the youngest, who is the best kid.
I talked to my other half this morning, when he gets home in two weeks he's gonna have word to his Dad. He knows how nasty his mother can get. I have a list ready. I have the ability to right people off, I do want to be careful not to do this completely for my other half's benefit. I WILL NOT be answering her phone calls. Nor will she be invited in without my other half being in the house. (thank you, guess i needed a little help to have a bit of strength to do this).
My other half has been pretty good at laying down laws, but the harrassment is only when he is away. Maybe not really harrassment, but certainly feels so. I will be reminding my other half of the legalities of stalking i think. Again thank you