Can my godchildren's father fight for custody of all his kids?

Hello. I recently found out that for several years now, my godson and his 15-year-old sister have known about their mother's multiple extramarital affairs. This is just one of the many things that were discovered to have been happening with the children including leaving her 15-year-old daughter alone in the hotel room in a foreign country to go on a date with her current paramour and bringing all her children (ages 17, 15 and 9) on dates and car rides with her current lesbian lover. Worse of all the 15-year-old daughter saw sexually graphic materials in her mother's phone. There were several videos of her mother engaging in a sexual act with another person who is not her husband, sex messages between her mother and several romantic partners, and sexual photos of other men's sexual organs sent to her mother by several men as well. Their mother has also left their residence and has been living in a condo since September 2023. This is the same condo where sometimes all her children and her current paramour would stay. The mother has no idea that the 2 oldest kids know about her indiscretions. Can their father fight for custody of his children?