Should I pay my narcissist brother back?

I know the feeling of being the scapegoat in the family. And having anger taken out on me rather then the person they were upset at. And others getting special treatment, etc.

My advice: Be true to yourself.
Don't try to tip the scales of justice one way or the other with your behavior and choices, or excuse your behavior and choices because someone else got away with it, or because they are a crap person. It's easy to feel like you want to make.life fair by taking. It's very easy to take this too far. To take and take and take to try to get what you feel you are owed because people abused and took and took from you. You can get yourself in trouble on that path. So be careful.

Do what is right to you for your own sake. Pay him back or don't for your own sake. Because no matter what you do, they'll be reminding you that you are thief until they die. They won't care of you try to make it right or not. There is no winning by their standards. So you have to decide what is good for your own wellbeing here.

At the end of the day you have to live with your self and your decisions. That can be hard in the moment with emotions running high. And knowing they are crap people.

Objectively speaking: Do you want to be someone who does not pay someone back? Or do you want to be the kind of person who does pay someone back?

You stole from him?
Yes.
His issues are no reason for you to be that person.

Paying back a narcissist is like putting out a campfire with gasoline.

You must write him an IOU, and when you have the money, pay him back the actual amount that you stole from him. WITH the IOU, write a short note of apology, explaining why you needed the money so desperately.

Ignore his lies about the amount. He is not a good person because he steals regularly.

I advise you NOT to use a cretin as a role model.

If you stole it you should return it unless HE owes YOU
Didn't matter what his situation is with others

Two wrongs don't make a right.

Hmmmm, this is about you... right? I know it's easy to justify one's actions by saying well, look at Johnny (or in this case, your brother), but it does not change what you did.

This sucks

I advise you ask for forgiveness and if he does not allow it, return it respectfully

This is sad to hear because he should be helping you if he has money

Only if it makes YOU feel better. You will never, ever, in a thousand years be absolved of your sin where they are concerned. With narcs, you're unable to be absolved of sins you DID NOT commit.