I haven't seen QH1. Read somewhere that Tanveer has a son. Rehaan had mentioned to Asma that he was adopted by Tanveer. So is he Tanveer's son? Maybe even Rehaan doesn't know that.
Yes I think Rehaan is Tanveer's son and she is asking Badi Begum about the will for her son's sake which is Rehaan. I think Rehaan will turn evil later, for now I don't know weather Rehaan is aware of parental identity.