It's important to understand that "hamari behen betiyan" is not a good way to solve rape culture. It is in fact, a furthering of the same patriarchal thinking that turns women into territory to be protected or conquered. See women as people first and foremost.
To not do so is to play into the same system that creates the problem. A system where a woman is something to be occupied, controlled, fought over, and preserved as a vessel that holds a family's or a society's honour - an honour that can be stolen or destroyed.
The word "behenc**d" comes from the same system that the sentiment "behenon ko bachao" comes from. It is the reason the troll goes for a mother-sister insult to attack men. It is the reason honour killings happen and it is the reason girls are banished from their families for marrying outside their religion or caste.
Sure a woman is a sister and a mother and all that. But even if she were not, she is worth every protection we offer a mother and a sister. Women's safety is a cause that needs to be freed from the vocabulary of patriarchy.