What do I do?

My kid, "Jo" has married a very manipulative, angry, compulsive liar I will call "Pat." Pat will lie about anything and has fabricated some very foolish stories. Pat was very ill as a child and always got what he/she wanted. As an adult Pat will lie and manipulate to get what Pat wants.

Right now Pat and No are renting from my elderly mother. Their pets have destroyed the place and Pat is demanding that things be replaced. I have refused to do so and No understands, but Pat is beyond furious. Pat and No are wanting to adopt and Pat claims I am preventing them from doing so because the destruction needs to be fixed for a home study.

I of course caved in knowing that the pets will again destroy what is replaced and knowing that my elderly mother will be manipulated. The thing is I know that Pat and Jo have not even started the adoption process, but Pat has fooled Joe into thinking that Pat, (a social worker of all things), can get them a home study in the next two months. I am angry that Pat is going to suck my mother dry repairing the pet damage. I am angry with Jo for enabling this. I am angry with myself for caving in.

Normally I keep my distance and let the lies go, but this one is really ticking me off. I see no end to this. Last week when Jo got pneumonia, Pat threatened suicide and then got pneumonia too. Three weeks earlier Jo claimed to have diabetes after Jo was diagnosed. Pat claimed to have been threatened in a coffee shop, when Jo insisted the cops be called Pat said no so went over to the coffee shop and of course nothing happened and it was Pat that became furious.

How do I deal with this? Pat has a vindictive streak that has resulted in going before a judge for threatening a child, has called the police and tried to have Jo arrested with false accusations, has claimed to have been kidnapped twice, (again I have no clue how we got to be a social worker). I don't want my mother hurt in all of this.