My Art Book!

So I made an oc near the start of this year and I actually kinda liked her design. I didn't think I would continue using her for anything, but I've been thinking I could use her more.
So I started thinking of a good backstory for her and I got one. Then I made a reference sheet, and this is what it looked like:

Yeah I named her Liz:,3
But I made her backstory and while making it, I thought of giving her a brother.
But you seE-

I can't think of a good design for her brother.
I've tried so many different ideas but I can't find a good clothing choice, hair, name, or even colour scheme.

Hold on I'll tell you their backstoryXD:
(Slight trigger warning?)

Liz is the older sibling even though she's shorter, but only by 1 year. As kids, they were mentally abused and physically abused by their single alcoholic mother.
Liz's brother hated their mother with a burning passion, but Liz didn't know what to feel about her.
Their mom still gave them food on the table, but the two siblings could tell that their mom never liked them.

But one day, Liz's brother snapped after being physically beaten. Her brother was 14 at the time and Liz was 15. Liz's brother finally had enough with their mom's drama and decided to run away from home. Liz protested against this, saying how they would never survive since they were both so young.
But Liz's brother eventually convinced her.
That night, they both packed their bags and tried to sneak through the front door with their mother passed out on the couch beside them. But when they opened the door, the door squeaked really loudly.
Their mother woke up and saw what they were doing. She tried to stop them from leaving because she was scared they were going to tell the police about everything she did to them. But in her drunken state, she pulled out her gun and attempted to shoot them.

They both avoided the bullets or serious injuries, and ran away.
Currently, Liz is 19 and her brother is 18.

So ye that's the backstory. (If something doesn't make sense please tell me;-;)

So I was thinking I could make her brother's personality to be cocky and "cool" but not really mean. He's really nice but he just acts really cocky. Idk if that makes senseXD
He seemed a little boring so I thought of giving him either multiple personality disorder or bipolar disorder.

But again, I don't know what to make him look like or what his name should be.

Please help;-;