For your age especially, don’t worry about school as much, nor a partner. You will only get your heart broken. Find new people, like people who understand.
For your parents, I’d suggest you show to them how much you care and share your thoughts with their relationship with you.
For the brother, and most of:
Just know he loved you. Every moment he was alive and every moment he’s gone. Don’t dwell too much on the past. Grief is not something that you can simply ignore. After my parents died and my sister was diagnosed with terminal breast cancer, I’ve been dying mentally.
Take your time. That’s all I need and can say.