Lostinside, what you describe is so sad. I fear you have little power to "rescue" your parents from themselves. Perhaps the best you can do is gently urge them to seek help for themselves, and that is something they must do for themselves.

Try to be kind and calm. As best you can, do not allow them to drag you down with them. To be of any possible help to them, you must be secure in yourself first.

May you find friends and allies.