I'm afraid this is going to get a lot worse before it gets better. Any time someone passes and leaves an estate, there's a strong opportunity for beneficiaries and interested parties to get into some serious conflicts. Your grandmother hasn't passed, and there's already conflict starting.

If your grandmother does not want to (or "isn't allowed to") walk away from the house and its mortgage (while living literally rent free until the foreclosure process goes through), you are going to need to protect yourself. You should start planning that now. Speak to an estate attorney now, and figure out what you need to do to make sure that you personally are able to reject being a beneficiary of the house, hopefully without also having to turn down beneficiary status on anything else. Maybe there's a way that you can have your "share" of the property divided equally among the other beneficiaries as a gift?

No matter what happens, you're going to have to personally "let go" of some proceeds of the estate, and you'll need to do it without holding a grudge against your siblings.