It is so hard to give others advice. One thing, however, stands out about your situation related to my own experience.
I am 60 years old and have dealt with the addictions of two family members living in my home over a 12 year period (off and on).
What I discovered is that the guidelines that we hear about in 12 step programs for codependents are as hard to implement as it is for the drug addict to stop drugs.
And, at 60, I seem to have finally "gotten it"... it took me that long. I, too, wanted to say I tried everything. The last things I tried were letting go, setting boundaries and focusing on my own life. Interestingly, these are the things that got me healthy and set up the circumstances for my addicts to figure things out (or not) as responsible adults.
I am not insensitive to the mental health issues. One of my addicts also suffers from ADHD and anxiety. And, in my family there is other profound mental illness. The thing is, adults are responsible for their health - mental or otherwise. I know people with various mental disorders that manage them and those that don't.
In terms of being able to tell your children you did all you could to keep your family intact, I suppose it matters what you mean by intact. Dysfunctional environments can sometimes be remarkably stable, right up to the point they implode. So, I'd think a little about where you put your energy and what environment is most beneficial for your children.
After all that, none of us can do any better than where we are developmentally. It seems to have taken me until old age to get a clue, I hope you are a better student of yourself and your life than I was.
Prayers for a good outcome.