Bigamy and property dispute

Name: RAHUL Email: Query: my grandfather died in 2006; without any will. he left 2 widows, 2 sons and 4 married daughters. my father the youngest son of my grandfather is also possess bigamy. i m the son of 2nd wife. ' actually due to unacceptable behavior of my step mother. my father married with my mom having consent of my grandpa. against which my step mom filed a case against most of family members. in a result family tension prevail. but after having a great discussion and with mutual consent she became affirmative and ready for arbitration on a condition for some 10000rs about 28years ago.after that both of wives of my father have been living under the same roof for 25 years. but now when we are looking for a bridegroom for my sister. the intention of my step mom and steps brothers derailed from its path. they are threatening o break the arbitration and to file a property and bigamy case. therefore, sir my question is what can be my legal powers to nullify their intention when father is in our support. as they are refusing to cooperate as the jealous and timidity has deeprooted bcoz we r aspiring for education and they are illiterate and jobless.Help me sir