How to get a roommate who is on the Mortgage agreement to move out?

We are only 6 years into a 30 year mortgage on the house. The other couple had a child and then decided to get a divorce, but stay living together because of the mortgage. My boyfriend and I are kind of afraid to leave our room because of all the yelling. Is there a way to get them off the mortgage so we can have another friend move in instead?
Added (1). Edit: They want to foreclose on the house, which would destroy our credit and cost my boyfriend his security clearance and career. We want to stay, but can't afford the buyout because the house is $70,000 upside down with no equity. We are trying to find a way get the mortgage transferred from the joint ownership to a single ownership, but the bank won't let us refinance.

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