Tenancy agreement and revision of rates

Dear sir/madame My question is what recourse do landlords have against tenants who refuses to accept revised rates in tenancy agreement. I am from Assam. My father who owns a commercial building has recently expired. By default me and my mother are successor to his property. Upon doing a careful research we have found that one of the tenants who has been in occupancy for the last 25 years and neighter has been a defaulter has been paying rent far below the market rate. Upon having a discussion with said tenant and offering a resonable hike, he refuses to accept the terms and wish to continue with the same rate he has been paying. I believe the agreement he had with my fathers stands inoperative upon my father's demise. I intend to have a fresh agreement with a revised rate. The tenant agrees to have a fresh agreement but refuses to accept the revised rate as per the market value. I fear that he might approach the court of law and obtain a stay order against us.What right do i have as landlord, protecting my interest before the court of law. Further i do not have any reason to evict him either. My mother survive on the rent and its difficult to manage at such lower rate. Please advise on the proper recourse. Your advise shall highly be honoured. Looking towards a positive response. Thank you