Child endangermet by allowing 43yo to have sex/minor

Here is the situation and question. The male minor is 17. His mother has primary custody and has allowed an online relationship with a 43 year old woman, even allowing the woman to come to NC and spend the weekend with child. This has been going on at least 9 months, when the child would have been 16. The mother also has primary of another male child age 14. How does one go about submitting this to court or dss or someone to prevent further endangerment of these two children? At the minimum, the 14 year old has been exposed to this situation and should be removed. The two boys are under joint custody with the primary residence with their mother.

An action for a modification of custody may be filed, based on the change circumstances in the home, and the inappropriate environment the mother is providing for the children.