Marrying the daughter of a woman one touched with lust

Q: A person has been married since 16 years and has three daughters( 14, 12, 7 yrs) and a son (3yrs). One or two year before marriage his mother in law was intimating him after that they( he and his mother in law) had sexual contact but not intercourse (dukhool). After the marriage they did not have that type of relation. Yesterday he heard from some source that her daughter was haram for him, so his marriage is not valid with her daughter. In that case children are also not halal with him and his wife. He loves his family very much. At the time of marriage he did not know her daughter will be haram for this action. He is very ashamed for his action since that time till now and asked forgiveness from Allah. Now he is very much worried about his wife and children. His wife did not know about that. We live here alone, where she will go. It will be very difficult for my daughters and son to survive with separated parents. My question is, his marriage is valid or not. If not what can he do to save six lives (any kuffara). May Allah reward you here and hereafter for helping his children, wife and himself. I will wait for your answer.

Unknowingly giving up my time to the theatre hall for a holi and easter celebration

Q: I am a lecturer/ tutor by profession. A lecturer asked to use my lecture theatre time for something. I did not understand or listen to her properly what she wanted to use the lecturer theatre for. Without listening properly I allowed her. Later on, i realised it was for Holi celebration and Easter celebration. Have i committed a sin? What do i do to ask forigiveness from Allah on this? But then again, it was not entirely on me allowing it or no because that lecturer threate is owned by my employer but I was only scheduled to take a class during that time.