Child custody

Mutual consent divorce done 2 years ago.Child current age 6 years ,separation happened when child was 1.5.Custody with father and on mutual consent paper mother gave up all rights and also says the custody cannot be challenged under whatsoever circumstances. The main reason for divorce is extramarital affair and women got caught. Visitation of mother - once or twice a week. Now post 2 years of divorce and visitation the mother had moved to court for custody. In her allegations she has mentioned everything under the sky : dowry ,harassment ,money taken for buying property ,vandalism ,etc etc - completely baseless and the prayer has no alignment with the allegations - don't understand why ?! In between the last two visit something very peculiar has happened.Child is extrely disturbed refuses the mention of the biological mother. Upon questioning said - that the biological mother in question had fondeled with his private parts much to his liking and also didn't care when he objected.The Child stands extremely disturbed and currently visiting counsellors.The custody hearing is due soon for hearing.What could happen in best case.Request help.