Legal openion

From your query, it seems that the land wherein the house has been constructed is stands in the name of mother, and so she became the principal borrower. Therefore, it is easly understand that the mother is the owner in the eye of law.

Though the building approval was given in the name of son, it will not create any title over the property.

On the other hand, (since it is stated in the query that the mother had no source of income) if it is able to prove that the property was purchased in the name of mother by utilising the fund of family and the same is  recognised by the Court of law, then the son also comes under the category of co-owner as one of the family member.

Sale deed is on my grand monther's name i.e. my father's monther.

Family money is not utilized to construct the house. Constructed house with my own funds. Have all the documents to prove it.