perhaps I misunderstand the question, but are you suggesting that one's body can discern whether steroids are legal or not? or that the legality of steroids might affect how they work within the human body?

My sisters after getting a Tumor removed. God put on some steroids. My bigger brother is a body builder and had a thing with the illegal ones. II mean he didn't act different but my sister is having a wierd reaction to the ones she one. So along the way there must be some part of your body who is like good steroids over here bad steroids over there. But if so how does that happed and is there an ingredient in all steroid like on the elemental or chemical level that could cause two different reactions and if so why?

you're talking about two different people taking two different types of steroid for two different reasons-- one of them with cancer... not to mention them getting those steroids from two different sources, one pharmaceutical and one from the black market...

there are lots of different variables here to account for that make this a bad comparison to start with and with far too little information to be able to give you any kind of rational answer.

Steroid is a broad term, there are lots of hormones that your body has naturally and that we have synthetic analogues of that fit into the steroid class.
Your sister is getting glucocorticoid steroids for her cancer. Those are antiinflammatory, they make your immune system slow down. They also have lots of other effects, like raising blood sugar levels, decreasing bone strength, and changing your mood.
Your body builder brother took anabolic steroids which basically act like testosterone.

You're comparing glucocorticoids and anabolic steroids - two very different things.

Glucocorticoids reduce your body's inflammatory response, which is why they're used for autoimmune/autoinflammatory conditions like rheumatoid arthritis. They also promote muscle loss unlike anabolic.

Anabolic steroids (as the name implies) promote muscle growth.

I'd recommend reading up on both kinds of steroids.