Mother (79) won't stop enabling my 50 year old deadbeat sister. My sister claims she is bi-polar. I'm not sure about the diagnosis but I believe she is using the bi-polar as an exuse for not holding down a job and bleeding moms money dry. Mom won't listen. my sister is on pills and probably crystal meth. Mom tries to cover for her all the time. The sister never helps with my dad who is in home care. Everytime she comes over she takes things from mom, food, toilet paper etc. I have told her to shop for herself moms house is not a store. My mom won't listen to me or my siblings. When we called my sister out on things She cries to my mom that we give her anxiety attacks for confronting her. We found out my mom has paid my sisters rent the last 2 months. We told her she better not this time, we will see. My mom is in total denial or won't level with us for help. We told her we will help, whe won't let us. Mom lives in her own home. The sister doesn't come over to Thanksgiving, or Christmas becuase of "anxiey attacks" I think she just can't face rational adults who know what she is doing. This is a nightmare when it is a family member who plays on my moms vulnerability and emothions. Plot twist, my ststers daugter always comes to my mom for everything too. I almost feel like abandoining the whole thing if I continue to be ignored.
As long as your sister is continuing to get what she wants from your mom she is unlikely to go away. And your mom is unlikely to stop enabling your sister. She's probably been enabling her for years. Trying to get your mom to stop is going to be like talking to a brick wall. These are behavioral patterns that have evolved over years. I doubt that you will be able to talk your mom into not helping your sister anymore. I think your only two choices are to either accept that this is the way it's going to be or abandon the situation like you mentioned.
But your mother can be competent, yet still be vulnerable. I don't think I'd want to walk away from it, in your place.
Your mother won't listen because you are telling her things that she doesn't want to hear. To take a few examples from your post:
deadbeat
excuse
"anxiety attacks" - specifically the finger-hooking inverted commas
My guess is that your mother wants to help her daughter, and is pretty sure that you have no such interest in helping your sister. She loves her daughter, but she's not noticing any love from you towards your sister. Every time she perceives an attack on her daughter, she's going to become more protective and therefore more enabling. That's no good to anyone.
The only way for you to get your mother to listen to your concerns about your mother is to change what you are saying to your mother about your sister. Try discussing your sister's, and your niece's, welfare and future in a less judgemental and more compassionate way, perhaps; and be patient about it because you're going to have a job convincing your mother that you're sincere.
By the way, it would help if you were sincere. What do you think would be a better, more effective way to help your sister?
I said "walk away" because you seem overinvolved in getting your mom to see how "evil" your sister is, when in fact she's mentally ill. Mom needs to understand, probably best explained by a lawyer, that she needs to set up a special needs trust for this daughter so that she can be provided for in the future, and not have mom disqualified from Medicaid.
If you end up being mom's caregiver, you will be consumed with ill feelings toward your sister. This, of course, is just my opinion, but give it some thought.
Did your mother find the experience frightening? If so, she could change the locks. Just for example.
I can't imagine that there would be any great difficulty in persuading the police and/or parole authorities to intervene if your sister's ex-husband poses any threat to your mother; and you wouldn't need your mother's permission to alert them to what is going on.
But, as you say, if he visits with your mother's blessing, and it troubles her not at all, then that is up to her. So bottom line: if you have a specific concern, report it. If you haven't, let them get on with it.
I tried everything through the years, tough love, compassion, reason, nothing had the slightest effect on my parents or siblings. It had become their way of life, just like you niece is now following in her mothers footsteps as a dependent mooch.
I finally detached from it all years ago, physically and emotionally. I suggest you also find a level of detachment that is comfortable and workable. You won't change this. Addicts will destroy everything and everyone around them to keep that buzz going.