[Skybird]

1. Approach in silence, observe, and collect more info.
2. If the collected data suggests it, strike.
3. If it does not, break contact.

For striking, you need to check out the situation yourself and not depend on hearsay only - even if it is coming from your nephew. You cannot look into your nephew's mind, and he may be effected by those girls himself in any way. Eventually you may want to engage a private investigator to scan the man's biography, especially regarding past school jobs.