Hello tillpost: I'm sorry you are caught in such a difficult situation. (I'll just mention, for point of reference that I'm a senior citizen as us old folks are typically referred to...)

Honestly I don't know what to tell you about your situation. My parents, many years ago, argued a lot too. Maybe not as bad as yours. I was an only child & we lived out in the country. On one of my birthdays in my early teens, my parents had a big argument about something. I can just recall getting on my bike & riding away telling my father at least I could have a happy birthday by myself. I had a girlfriend whose parents absolutely HATED each other! Anytime I was ever at their home, they never spoke a word to each other except every so often they'd break into an all-out shouting match! I don't know why these things happen... but they do.

I, of course, don't know how old your mother is. But since you're now 20, she must be at or around middle age. That being the case, she's had many years to become the person she is today. You can't change her. Nor is it your responsibility to try. You talk with her, as best you can, about what's going on & how it's affecting you, your sister & your mother herself. You've offered to see a doctor with her. That's about the extent of what you can do in my opinion.

It's certainly wonderful of you to be concerned about your younger sister's welfare in all of this. But, beyond trying to be as supportive of her as you can be, I don't know as there is a lot you can do for her either. Perhaps if arrangements could be made for her to see a counselor or therapist (assuming she'd be willing) that might be of some benefit. But, beyond that, you're a young adult yourself. It's time for you to do what you need to do to get the ball rolling, so to speak, on your own life as an independent adult. It may be that the best you can do is to simply take care of yourself. And in doing so, you may find you will be better able to be supportive of your sister to whatever extent is possible. I know it's not ideal & probably not at all what you might wish for. But it may be all that is left you. At least these are my thoughts with regard to your post. I wish you well...