"I could get away from them, but then who would look out for the ones who need it? Who'd be there to talk with and help my mom? Who would have my little sister's back and help her get through her own stuff?
I might be a failure, but I still feel like I have a job. I just wish I could find a way to succeed at it.

I just don't want to keep letting everyone down."

The fact that you just feel like that about your mom and your sister means that you are a very special person. But please remember, we can love others and it means SO much to them but we can't "fix" them. I say this because your mom made an attempt. So did I. My attempt was not caused because of my spouse or my children. It was caused because of what was going on inside of me. I had to get educated, get help and be motivated to change. I think I only became motivated because the attempt shocked me into action. My daughter makes me happy but my failures are not because of anything she did.
I also am learning to accept that I can't make their lives be a certain way. First and foremost, what can you do to have a positive effect on you own life? You will not let people down if you take care of yourself. You are worth it.