The problem is legal heir ship certificate of your in laws.
Since the property had been settled in favor of your husband by his father, it becomes his own property and hence there was no need to obtain legal heir ship certificate for your father-in-law's successors.
Subsequent to your husband's death, the property were equally distributed among his legal heirs i.e., you , your mother in law and your children. Since your mother in law also had transferred her share of property on your daughters' name, the necessity for legal heirs for your mother in law is also not required.
Thus on the basis of both the settlement deeds, you can get the revenue and all other records pertaining to the property, transferred on joint names of your children and you.
Therefore, as there is no necessity to obtain legal heir ship certificate, you need not trouble your sister in law residing abroad for this purpose.
Discuss in depth about the necessary formalities in this regard with an experienced advocate.