I had stayed with such a person before, but not my brother in law, it was a friend of my hubby. Her family chased her out of the house, she got no where to stay so we allowed her in for 1year and everything in the house went hare-wire!
its difficult for you to solve this, cos' you are but a sister In law only.
Have you told your hubby about how serious this problem is for you and your pregnancy?
Let your hubby talk to your brother in law. If he really can't. Then YOU write a letter and pass it to him. Let him read your concerns.
The thing is dont't feel because he is related, and that you should give face, cos' that's how most problem dont't get solved eventually.... not asking you to be crude , just write down what EXACTLY goes through your mind....
go talk to your hubby first. If hubby doesn't want to talk to your brother in law, then go write that letter of yours.
I'm not trying to stir trouble, I'm just relating what WORKED for me before.