The concerned property is held jointly between me and my mother, we are joint owners. We want to sel

The concerned property is held jointly between me and my mother, we are joint owners. We want to sell our property but the property can only be sold to my cousin who is living in the other portion of the property. It is a partitioned house separated by a common wall. My grand mother's will put the restriction that we can sell the property only to her. I am not interested in selling it to her as she is offering a low price. But my mother has already taken an advance from her and signed an agreement to sell, I have two floors above and I want to give it on rent, but my mother is not interested. Whenever someone comes to see my place, my cousin tells them that the property has been sold to her so they should not come here for any rentals.

How can she claim ownership by just giving an advance? My mother has only taken an advance and not the entire sale consideration and she has only signed, not me. So is possible to give it on rent or no or despite my cousin's interference, who has only paid an advance? If i give the place on rent is my mother's signature also necessary on the rental agreements? A lawyer who I met locally told me that my mother's sign is not necessary, please clarify! Kindly advice.