Locked property illegally by brother and sister

Need your valuable advice for my relative. His father has gifted him one part of the house including 2 rooms at upstairs and it is registered in Registry office. Other part of the 2 storeyed building was occupied by remaining 2 brothers. Now his two brothers and his 60 years window sister locked my relatives 2 rooms at upstairs since last 10 years . My relative tried to resolve it through several meeting but failed to do it then my relative also locked over it. Now How can we recapture it? Can we occupy it by doing 144 dhara through Advocate? Can they file false theft case if my relative break the lock to capture his upstairs rooms? it is clearly mentioned in the Deed that no one can demand this part of the building in future except my relative whose father gifted it. Religion Hindu.