Mother lying to Father ruined her Brothers Marriage

[watching sidelines]

What if you new that your own mother lied many times to my father and did some really dirty things to ruin some ones marriage. What if you saw her open mail, hide mail, know about her incident where she gave a lap dance to a coworker when they were training and my father had no idea. Do you tell the father all that his wife has been doing or do I sit back and watch her ruin other lives. Her lies and cheating are getting to be to much and she won't tell the truth after I gave her the chance to come clean and fix all that she has lied and done.