I really want to know so please you guys should help me out.

Is there any relationship (brother/sister) between two persons, a boy and a girl given birth to by different parents( different Mother & different Father) but share the same sister??
I. E. The mother to the boy had a child for the girls father before she later got married to another man.
My question now is, are the two other siblings related?
I know the scenario will be hard to understand but I'm here to answer any of your question about it.

No. nothing deep