How can I get rid of her?

First of all, are you the only one in the family who feels like that? Or do you all dislike the woman? Is it difficult for your brother-in-law to pay these extra bills? Or is he rich?

All you can do is have a nice and long talk with your father in-law. Don’t be offensive towards the woman. Find out wether he really loves her.

Give him a chance to talk. If a man is in love, then he’ll not see any of the bad sides of a new partner. But as emotions cool down after a while, he’ll start to see her flaws.

Just make sure he knows he can come to you to talk about everything. Be a friend.

You can tell him honestly that the rest of the family isn’t getting along too well and isnt too happy with his new partner. He’ll defend her if you’ll be offensive, so try to be the mediator instead. Tell him what you do not like about how she acts towards the rest of you and ask him if you should do anything. Make sure he gets that you are criticising the way she acts because people can change the way they act. Make sure he knows that the fact that your brother-in-law is paying the bills bothers the family.

But - when your dad-in-law decides to stay with the woman, then that’s his decision. Your brother in-law can stop paying - he doesn’t have to do that. Or he can tell them he’ll pay only under certain conditions. For example only if they start applying for jobs (or if your father-in-law does all the housekeeping) only if the woman goes and gets a job. But you can’t force an adult man to quit the woman he loves.