How to stop brother from selling his share in property

Sir, my father has bought a land in 1988 with his own money. But due to his father's pressure, he had to register his younger brothers name along with his. During registration, his brother was a minor (16 years old). We have his age proof with us. Now the problem is, a three-storey structure on the land has been constructed in 1992 and my father beared all the cost. His brother is occupying ground floor, my father 1st floor and 2nd floor only structure is there, no room construction yet. He never payed a single penny on maintenance, water bill or tax. We are concerned that he might sell his portion (ground floor) to any illegal person as he is in talks to this kind of people lately. Please guide us, how can we stop him in doing so. And how my father can claim his rights on this property because he is the one who invested in this property from the begining and now also maintaining it.