Should the step father be obligated to pay for his step son's private college tuition?

I have a cousin. Her son is very smart. He got very good grades in high school and worked very hard. He got accepted into a private school and got a scholarship. The problem is that even after the scholarship a tuition of over 17,000 dollars a semester has to be paid. The mother can’t afford it. I sent them a couple hundred dollars, but that was all I could do. The step father make more money than she does, so she wants him to pay. The problem is that if the step father pays the tuition he’ll lose all his retirement money. She said that even though he is the step father he should act as the father and pay. The son’s biological father is serving a long sentence in prison and can’t do anything. She feels the step father is the only one that can do it. Should the step father pay for the step son’s tuition. If so, how can I pursuade him to pay?