Hi Thisdevotedheart,
Welcome to the Forum. I hope you can find some really good help on here and I think by just having a vent you will feel a little bit better.
I am not in the same position as you, but I am sure there are lots of people on here that can help.
The Icarus Trust is another organisation that could help you.
Could you go to your Mums Doctor and speak to them confidentially?
You are going through so much and at such a young age, you have your whole life ahead of you, I admire you for looking after your siblings.
I hope that you find some help soon. Keep chatting on here, it really makes you feel that you are not on your own.
Take care.
Dx