I kinda know how you feel, I have a really close friend (I'm also really close to her brother) whose brother has attempted to commit suicide several times, and I don't know how to help him and I don't know if I can help him. And now my close friend has also started to do self-harm and I feel so useless.

I'm sorry, I'm probably not helping.

Do his/her parents know about this?

The parents know the boy has tried to commit suicide several times, but they don't really do anything about it. And I'm pretty sure they don't know the girl does self-harm. Which just makes the situation worse...

Encouragement, love, and just simply being there are great places to start. If you go to school, find a teacher that you feel will help and care, tell them. Idk is this is helpful or annoying, sorry