One of my sisters is scared she will end up losing the house "and then what?!" With my nanna no longer around to enable her/bail her out it's quite worrying.
Don't be worried. Firstly, it's a situation she's bringing on herself so is nobody's problem except hers. Secondly, if she ends up homeless she'll be housed by the council in emergency accommodation until she's rehoused in private rental or housing association flat or care home, depending on her finances and health. It may be a shit situation that she hates but the system exists. So don't go feeling like either of you has to take her in if the worst happens.
A very simple example of projection I came across Must, two people I know, both women, both parents, let's call them A and B and the DC miniA and miniB. At the play park the DC enter at the same time, both A and B are there to witness this. As they go through the gate, miniA pushes miniB over deliberately and miniB falls. Immediately A snaps angrily "miniB! Why did you do that?!" placing the blame for the incident firmly on the victim. B is shocked into silence and left scratching her head about what just happened. They both saw clearly that miniA was the aggressor - but A can't accept her DC is anything less than perfect, so it gets projected onto miniB as being the problem child, while miniA gets away with their bad behaviour scot-free.
Another example is when an unfaithful spouse accused their faithful partner of cheating when they stayed overnight at a friend's place. Because that's what they'd do, given the opportunity. They can't understand or accept that not everyone is like them and are projecting their personality and morals onto their partner.
Wellies the other thing GB2s ranting to others does is it garners sympathy from them (he's upset, responding with sympathy is normal) whilst simultaneously deflecting from what he did/didn't do. It's manipulative. Especially when others don't realise he's lying about what happened. Even if they do, it might take them until some time after the ranting-and-sympathy occurs to realise he's the architect of his own demise.
Since nobody wants to be on the receiving end of his anger, it's easier to just believe his version and go along with the narrative that you're the problem, if they're going to remain in contact with him. Every FM action in pressuring you comes down to do what the problem person wants so that we don't have to do the thing in your place, or face his anger, or listen to him ranting about you. It's totally selfish.