Can in laws be implicated for husband cheating

My brother cheated his wife by bearing two children to another woman, who was a prostitute with blackmail cases registered on her Muslim name, he spent more than 25 lakhs of my sis in law, now he wants get rid of her by not giving a penny but our ancestral property, he claims he has right, my parents own a land British adangal later being called assigned land, it was given to our grand father in 1930 by Britishers, out of my dad's entire 2.5 acres, dad spent money he got selling 2 acres on my brother, so left half my parents want share between I n my sister, but my sis in law's are blackmailing us to give her the entire property as a favour for not implicating us,  how can we be implicated, we stayed away from him, since we knew, and stood by her going against my brother?