How can I secure full ownership without legal documentation?

I have two sisters and I am the only son of my parents.

- Neha Pathak

In 2010, my father and I jointly purchased a property in both of our names, with 70% of the funds provided by me. Later, with my parents' approval, I transferred the corresponding share (based on the 30% paid by my father) to my sisters, but I did not create any legal document for this transaction. My father passed away and all of us siblings had his share in all his assets transferred to my mother (including the 30% of the property jointly purchased by him and me). I am concerned that in case of my mother's demise, will my sisters have any right in the 30% share? We are a Hindu family. How can I secure my claim to the full property ownership, given the lack of documentation for the transfer to my sisters?

-Name withheld on request