Touching one's mother with lust
Q:
1. I know that if someone touches his mother with lust, it will break his parents marriage. I want to know if it is permissible for his (the one who touched his mother with lust) children/grandchildren to marry his brother's/sister's children/grandchildren? Are their children/grandchildren allowed to marry each other?
2. Can he (the one who touched his mother with lust) marry his mother's brother's daughter?
3. If the thought comes to mind that a perosn touched his mother with lust during his childhood, but he is in doubt whether he touched or not. What should he do now?