bigamy case, mental harassment, blackmailing.

Sir 5 years back my brother allegedly married a girl without telling and absence of family members and friends. that girl has photos as proof. my brother was mentally depressed and on the blackmail of her he agreed to get marry on the verbal mutual agreement of not harming each other( which we don't have any proof for this). on this verbal agreement my brother got second marriage without knowledge of bigamy in front of family marriage and friends. now both first and second wives together blackmailing him to lodge a bigamy camplaint. what should he do. both wife has photos as proof but not legally registered. Please advise on this.