Flat occupied by family

Hi there, I’m an NRI, possessing a property( a 3 bedroom flat) in U.P. Its registered under my husband’s and my name and we have a copy of registry as well. My brother has been using this property for last 10 years, there was no formal agreement between us. He wasn’t in the financial condition to pay the rent to us so it was never discussed. He then moved to a different location and relet the flat and used all rental income. Again, in good faith, we let him use the rental income as he didn’t have enough earnings to feed for his family. Now he moved back and wants to live in the same flat with his family. We have a suspicion that he wants to illegally possess the property. When we asked for keys for the flat, as we now want to sell it, he started to give excuses. In fact, it turns out that my father is also in his support. We have exhausted all options in resolving the matter at a family level but all efforts failed, now looking for some advice on where we stand legally in this. Thanks,