I'm going to steal back money from my brother
Why do you want to steal back money?
My brother used some money I had stashed, and I found out later.
It's reasonable to take back money if someone has owed you for a long time. Otherwise you might never see that money again.
I can not believe my brother stole from me. It is unbelievable.
What he did is really wrong. You should also tell your parents what happened just incase he accuses you of stealing from him. He could have stolen that money as well and if it came from your parents you could be blamed.