How can I get my niece, her boyfriend & 4 kids out of my elderly mom's house? I fear she's in danger & doesn't see it!

I wish I could say that this is not a common problem but I have seen it play out more than once. Hopefully your Mother will listen to you or give you POA.

You need legal advice. If your Mom will not do it, you will have to get an attorney to convince her to evict them, or give you POA and you do it. I feel sorry for those poor children. I will pray for their protection. First thing tomorrow, call an elder law attorney and nip it in the bud. She may be intimidated by both lowlife adults and feel badly for the children. I am sure she feels helpless and confused, and it is an unexceptable environment. Let the law work for your Mom.
All the best, Lori. Let us know how it goes. Hugs and Peace.