House been Illegaly Seized

I belong to a town in Uttar Pradesh. In 2010, my Father purchased a house in partnership with one of his friends. Uncle had requested my dad to buy that house with him as he was unable to afford the full amount of that house in which uncle was living from past 20 years. The registry was done in name of both the parties (My Dad and Uncle) with 50%-50% of land registered in name of each party. As we were living in U.P. the house was taken care by uncle's family, we some times used to go and stay there. In 2012 uncle expired, we didn't discussed about the selling of house till this year. Uncle's son was offering a price half the market rate, on which we were not ready to sell, talks were on from past few months. This month when my parents went to the house, they didn't allow to enter us, they had changed the locks and proclaimed that they have Seized (Kabza kar liya) our portion. No one in my family have been in such situation before, we are looking for some expert legal guidance for this case and how we can proceed on this.