How to stop father in law from selling our land

My father in law is drunked and gambler and irresponsible for family and my husband is job holder and once is got job he took all the responsibility and struggles a lot from childhood because of his father. But now my father in law told he has dept of 15 Laks and trying sell the land (which is from his father not earned by his own) with out our knowledge. How can we stop this. Pls advice. Thanks in advance