Property rights

1. This is a case of "private adoption" where they need not to have followed HAMA / CARA guidelines as to "legal adoption". It is valid being private adoption.

2. Inclusion of their names in Ration Card and other public documents and well treatment of them as their own children by your In Laws itself is 'compasionate grounds" later on to inherit share in ancesterol property and even otherwise your In-laws know very well DIL thought process and may will give share of property to these two children (now turning major as you say) and in that case your husband / your children cannot even challenge much other than their share they may get which are all too early to make legit via Court as your In Laws are still alive.

3. An adopted child is deemed to be the child of his/her adoptive father/mother for all purposes with effect from date of adoption. This is aslo case in "private adoption". All the ties of the child in family into which he/she was born are thereby relinquished. The adopted child is not divested of any property already vested in him before adoption. An adopted child would inherit property of his/her adoptive parents in the same manner as their natural child would do. Under HAMA, the adopted child has the right of collateral succession both on his adoptive mother's side and adoptive father's side. All persons are entitled to succeed him as if he is a natural born child of that family.

See if everything is going smoth between you and your In-laws and your husband till date never had any objection to his parents adopted childrens / so called wrongful adoption then why you are getting worried? If it is property inheritence question of your children then your In Laws are still alive + your husband is still alive let him inherit his share first and at this moment you raise your doubts the In Laws may pop some hidden registered will that they already have prepared long time ago sensing future DIL issues.