Builder issues

Hello All, I would like your advice regarding my new house problem. In late 2016 my dad and uncle started to construct our house. The work was given to a contractor who happened to be a friend of an acquaintance. No formal agreements were made between us. After a while there were delay of payments from my uncle which led to the stoppage of work at the site. This led to an argument between my dad and the contractor. We made some payments after which he resumed work on the ground flood and first floor (our portion), but stopped work in the 2nd floor (uncle’s portion). In late 2018 my uncle entered into a lease agreement with a party to finance the construction. We even finished the house warming ceremony. Now when the lease folks want to move in, the contractor has increased the bill both for my dad and uncle and has locked the house. I would like you to note that both my dad and uncle are senior citizens. I am really concerned about the state of things and would like to know if and how the contractor can deny entry for us in our own house and what legal angle can we take to prevent him from doing so. He has given a receipt for only partial amount of the overall paid sum. Looking forward for your valuable inputs. Thanks & regards, Guru