Group got a plot but did not register. what are the consequences

18 years back my father had a group with 12 members in it. as the group got registered in that year, even they got a plot of land around 12 Bigas, due to some problem they didn't registered the land in their group name, and some years later without consulting with all the member in the group, two members registered the land in the name of a person who is never known by anyone . now again they sold the land to a man and he too registered the land in the name of a group, interestingly this group is not registered or he just put the name(the group doesn't exist).now i want it back as it was b4