My son's girlfriend will not allow my son to visit- Lease States 'No unauthorized guests allowed'?

This is in Pennsylvania: My son’s girlfriends Landlord has taken a dislike to my son. My son is 39. He has forbidden my son to be able to visit his girlfriend at her apartment. She has a lease that states ‘No unauthorized guests allowed’, but that sounds a little vague. When his girlfriend attempts to speak with the landlord he intimidates her. Her son in law is a police officer in the same town, and I’ve suggested that he (un-officially) attempt to speak with the landlord to find what the issue is. If anyone knows PA law, though, and my son goes to visit, cops are called, my son gets arrested for trespassing, then there’s court costs, etc etc etc. Anyone know PA law on this? Thanks!