Aushin, you seem like a really nice person. And I love that throughout this thread you have been open and willing to say, "oh yeah, didn't know that, thanks". Much respect.
But (you knew the but was coming, right?). This situation isn't tenable.
For one thing, you are effectively training all these people to rely on you for everything. Not just housing, phones, but also to solve their problems like the leaking fridge. Having set that situation up... what will happen if you get hit by a bus tomorrow? Seriously? You seem think you are the only one who can help them... and if you really think that is the case then you must see how risky that is.
Don't just go and fix the fridge. Show them how to fix the fridge. "Give a man a fish and you feed him for a day, teach a man to fish and you feed him for life" needs to become your new motto.
There were a few things that really stood out to me in what you've said:
I sort of expect to be supporting my mom and uncle for the rest of their lives. My sister and her baby I'm not sure. Depends on if she can find money elsewhere.
But if you keep giving her everything she needs, why would she bother to look elsewhere? She won't find money elsewhere as long as it is coming from somewhere. Do her a favour and get her out there and working now. You're making her life easier now, but setting her up to be 45 who has been unemployed for 15 years, which is a hell of a lot harder than a 30 year old who's been unemployed a short while. (Ages made up for illustrative purposes).
I don't know much about your laws (in the UK here, where she would be protected by the Rehabilitation of Offenders Act), but is she really unemployable because of drugs offenses? I am led to believe that the US rates of incarceration are very high, so wouldn't that leave an awful lot of people permanently unemployable? What are they expected to do (I mean by the government. Because there must be something, even if the answer is to let them die homeless. Seriously, what do the government expect ex-cons to do?)
And a later quote from you, regarding your grandmother and uncle: "she has a probably-not-healthy relationship with him, where
she has shielded him from all responsibility for all of his adult life."
Who does this sound like? You recognise where your gma went wrong, and yet you are doing exactly the same thing for/to your mom and sister.
You also say " I don't think I have a savior complex." and yet "the ship wouldn't magically find a way to right itself if I unplugged the hole. I am very literally presented with the choice of supporting them or letting them all be homeless. " So you do think you are singularly responsible for them...
As with other posters, I'm not trying to be mean, I'm trying to be realistic.
The way I see it is either:
1) You are not the be and and end all to their survival the way you think, and they would get along without your help
or:
2) you are the only thing between them and destitution
in which case you really do need to do something about it because it is very precarious to have 5 (?) people depending on one persons health and job security.