I don't want to help my step-sibling out financially.
Have they wronged you in some way, is that why?
Because I don't feel close to them.
You don't have to feel close to help someone, but you're also not obligated to help them, either. It's really just a matter of choice.
They are only asking me for help because they know I have money.
I imagine that makes you feel used. At the end of the day, it's your money, so you do with it as you please.