Lease agreement signed by my father not alive now. how to challenge it

My mother and father is having ajoint property with my father's two brother and there two wife's with equal share of 20 marla each total 6 kanal. My mother was died on 25/11/2004 and the virasat of my mother share is transferred three legal haiers including my father in 2005 now we are 7 partner in property and no devidation is done but after some time 5 partner leased 8 marla each total 40 marla to hpcl without my and my brother concent and the area given to hpcl is demarked by 5 partners and they signed the lease agreement but after that my father also died in 2010 now should i challange