Need advice for handling a difficult sibling. What do I need to do to protect MIL and ourselves from these crazy people?

My husband and I had to take over the care of my elderly MIL from my SIL.

A little background...My husband and I lived in another state. My SIL was continually asking to borrow money for my MIL's medicine and assistance to pay her property taxes...which we have done for the previous 5 years.

My MIL's property was paid for. She has almost 3 acres and had a tiny 3-bedroom trailer. Between her SS and husband's pension, she should have been able live comfortably.

One day my MIL decided she was going to run away from home and come to TX. Thinking she just wanted a break, Hubby drove to her home, picked her up.

He was shocked by what he saw.
The property had been overrun by junkies.
Her daughter, daughter's ex-husband, 3 children, their spouses, and 3 great grand babies, were all living on the property.

The trailer was in shambles with holes in the walls and floor, 5 outside dogs, 11 inside dogs, grass 4' tall. Drugs growing in the garage... you name it...

They all had money for drugs, cigarettes, and alcohol but no money to pay bills, or purchase mom's medicines. They ran up her credit cards, ran the phone bill so high it was shut off.

SIL also even now bullies "mom" into giving her money. We aren't looking at 40.00 here and there, sometimes it's hundreds...with "I have to have it"..with an "or else" tied to it. Or else I'll be sleeping in my car, I won't be able to go to work,..etc" yet she always has money for pizzas, fast food, taking her grandchildren skating, running around with friends, staying in hotels, etc.

MIL did not want to leave the property permanently - as her husband had died there.

Anyway, Hubby moved to her place.
He made it as uncomfortable as possible to stay there. Phone was shut off, (put mom on ours), cut off TV, power to their camper. After a few calls from Social Services, and literally physically assisting the police with arrests...they all left.

1.5 years later, hubby had the property cleaned up enough to put a nice double wide trailer on it and have a septic system installed. (Here a lagoon is all that is required).

Yes, the property is in MIL's name with my husband as the beneficiary. MIL and we also are making payments.

MIL's care became difficult for my husband so, I retired from my job, moved "home".
I take excellent care of my MIL. In fact, she is spoiled and with God as my witness she deserves it.

People drive by our place now and actually stop to tell my husband he is doing an excellent job and that place is looking so nice.

The local first responders (who were out here many times -not for MIL - for calls that were drug related) have mentioned some of the things they observed and have expressed their relief that MIL is now "safe".

Problem: my SIL and Niece (neice is now clean) have been telling relatives they are going to sue us for the property when mom dies because FIL verbally promised the property to them.

Do they have any standing? I wouldn't think so but I don't know for sure.

BUT, my SIL is very conniving. I don't trust her. When she comes over, things disappear, mom gets stressed - starts looking for money in her wallet, (without telling us "why"..which we already know.."why"...) and

Now she is trying to take mom out by herself "just to be with her".

Mom does not have a will, but has made my husband the beneficiary to her life insurance and property.

MIL's memory is really poor. She will ask me 15+ times while we are waiting at the Dr.'s appt. why she is there. I always answer, never raising my voice and always behaving like it's the first time she's asked...because to her it is.
SIL will take advantage of her memory issue whenever possible.

Suggestions?