C,
I know where you are at right now. I just had to let go of my addication of 18 years. I tried to fix him, but you know what I cannot fix him. This is his fight and when or if he shows me that he has changed, not with words but with his actions. Remember words are not worth anything unless the show they have changed you are going to think why or what did I do wrong.
If your older daughter does not understand now, one day she will see what you were doing to better your life. They do get sooner or later.
As for the younger ones teach them how do things that would help you out. Even if it picking up dirty clothes, or picking up there dishes.
Take the depression one day at time. Look in the mirror and say this is going to be a good day. Smile. If it is not a good day then let your kids know that you have had a bad day and need time alone. They will not break.