بسم الله الرحمن الرحيم
(Fatwa: 396/348/H=03/1435)
They are not your real parents. They adopted you and brought you up and got you married. It is a kind of favour and benefaction on their behalf. It is not wajib for them to transfer the property in your name and deprive their original heirs or to give them less, rather it is unlawful for them to deprive their real heirs and give all property to you. Your step parents are yet alive and in their lifetime they have full right over their whole property. They possess the right of hibah (gifting), waqf, bai’ etc if they want. The ruling of inheritance shall be issued in their property after their death. We may write the Shariah ruling if we receive the Shariah detail of their heirs, in-shaAllah.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband