Can parents take away your disability money?

Once I turned 18, a portion of my stepfather's disability checks were deposited into my bank account under my name. Every month, my mother and stepfather forced me to withdraw the money and give it to them. I have always wondered if this is legal. My friend was in a similar situation, however, she had kept the money for herself every month, because that is what her family advised her to do. Please let me know if what my parents did was legal, I am unaware of all of the rules that go along with this, and am unaware if this money actually belonged to me or to my parents like they said.