Query to know the legal process

My wife is owner of a first floor in a residential freehold property in delhi vide registered gift deed from father. Currently she is not staying in this property and her brother is staying on ground floor of the said property. Although the property was gifted long back to my wife by her father and during his lifetime her father was taking the rent of the first floor which belong to my wife and she had no objections to it. Now recently her brother who is staying on ground floor has given her first floor on rent without her permission by executing a rupee 100/- stamp paper rent agreement( un-registered) on his name. My wife values more to relations than money, so she still have no objection that her brother takes the rent of her floor but at the same time she would like to know from you experts that going this way, will anyway create problem for her to claim her ownership of first floor in future in the said property. She questioned her brother verbally and he said that he is just continuing the way as it was during their father’s lifetime. My wife even offered to her brother to execute a registered rent agreement between tenant and her and she would give the rent received to her brother by cheque but he refused saying it is too complicated. She really don’t know the intentions of her brother. Please guide, if at this moment she need to follow some legal process to safeguard her interests.