My heart goes out to you.
Seeing the constant dysfunction of family while trying to have some kind of reasonable life is always so hard. Congratulations on your accomplishments - you have fought the battle and strengthened yourself. And I don't know what you could possibly do to make the situation better because the people who must choose better are not doing so. But you are choosing better.
I heard a quote the other day - "you didn't fail, it's just time to let go" Oddly, it was on a TV show but it just jumped out at me because I have a whole set of crazy family members (addicted and not) that do stupid things over and over. I love them and have concern for them, but they never seem to learn despite my best efforts. So - maybe one way to let go of the resentment is to realize, you have not failed in any way - it might just be time to let go of it all.
For me, resentment is always a sign I have more to let go of.
Best wishes and prayers.