My brother in law having an affair

Hello sir my concern is my brother in law is having an affair . All the family members and her children everybody knows about this from past 10 years . But he always denies it. And he is alcoholic and a government employe and my sister too. Her daughter is 24 years old and son 20 years old. His behaviour has been arrogant, hostile and jarring which has results in my sisters series of health issues. His behavior toward my sister is really cruel domestic violance , alcoholic misbehaviour, mental harassment and loss of self esteem and dignity due this insulting, use of bad language and verbal further.and girl to whom he have a affair she's also a government sister doesn't want to divorce but she want to teach a lesson or punish them Her husband and that lady.her daughter is unmarried and her boy is still studying and he denies to give study expenses to the children.that women is already divorcy and have 2 boys. We have pictures of my brother in law and that lady and also voice recording ..please suggest something sir