My niece always talks about when my Mom passes. How can I get her to stop talking about this?

I live with mom and monitor her diabetes and other health conditions. She is doing well. My niece (24 years of age) and her husband moved in with us as they couldn t afford their rent. Mom bought them a new car as a wedding gift. She also bought my niece a new camera and I pad mini with which to make you tube videos. She is also a cna. (I am a nurse and encouraged her to do this.) Her husband got a job as a plumber assistant and is going to school to get his plumbing license..She stays here and makes videos..She wont work as a cna as she cant handle the abuse. She also has a shitzhu puppy who she doesn t feed (we do mom and I)
Also she tries to get me in trouble with mom so mom will throw me out and she and her hubby can get the house!! To top things off, I called her mom and asked her to talk about what we would do if mom passed down the road..She had a fit and called mom and told her that I cant wait for her to die, etc. My niece sat across the table from me during the whole conversation I had with sis (who is also mom s favorite even though I ve done everything for mom..) she is also very abusive to me which is why I dont contact her...my niece kept asking "why did you call her? " I said to at least include her and give her the benefit of the doubt". Mom wants everything split down the middle...which isn t fair as Ive been caregiver for years...sis just calls every day and asks for money and mom sends her at the least $5,000.00. She also emptied out her safety deposit box of $12,000.00 and sent it to sis in Calif. (We reside in Florida). Sis has complained for years that I spend all moms money... when she s the one doing it...!!! Getting back to my niece, she wants to have her babies here with me to watch them while she takes over the house and I gave her a flat "there are some nice daycares out here" answer!!! She expects mom to foot the bill on everything and that she should help her granddaughter out as shes newly married!!! She also wants an inheritance!!!
I told her she nor I will get anything as mom is giving it all to sis and they both deny
that sis has any money. Mom keeps saying "thats my baby" even though sis cares less and never comes out to visit..only calls and asks for money..While neice keeps mentioning when mom passes I should have a plan and where will I go...I would like to keep the house but mom wants us to split everything...I think niece has a lot of nerve...I cant explain it to mom as she wouldn t understand and would only not believe me but blame me that Im the one who is wanting her to die...!!! Anyone else
going through this?? Any advice? Also I feel powerless that sis is draining mom s funds...there isnt much I can do about it...