Which proofs are required to prove nullity of marriage

I am writing on behalf of sister.recently we filed a case against her husband in 498a,506,420 ipc sections and the cases are with out counter yet.they are deliberately taking time for counter.The accused cheated my sister with false job profile and also harassed for dowry and used to beat her daily due to his alchohol addiction .We also filed for nullity of marriage due to no intimacy because the accused used to postpone intimacy due to unknown reasons despite of my sister's request .But he gave a counter on nullity of marriage recently that my sister is an alcoholic and had many affires at the time of marriage. But the fact is we do have evidence that he is an alchoholic,like pictures, videos and also documents proving that he was jobless at the time of marriage . What can we do now?can we filie defamation case on him? Will court accept our proof at the time of nullity case trail?