property for adopted child

dear sir i was adopted by my mothers's elder sister. i was not aware of these till my adolcent age. As per records school records , employment records my parents are my adopted parents only . but legal document is not there for adoption.

now my adopted fathers sister with the help of her brother suits in the court for inheritance saying that ther is no legal heirs for my adopted father. they cliam that i am donot have any right on the property of my adopted father. please clarify. Right  now i am the custodian /possessing the  property and my father died five years ago and my mother died a year ago. They waited all these days, and now says that legal proof is not there for me to hold the property. My adopted fathers property is only because of inheritence. so  i donot have any right on that.

please advice to e-mail.