So, I think the storyline is they discover his Father's photos which he took of a young friend of theirs. The implication being that the Dad likes young guys, however, this interesting storyline is never followed up. What a waste!
This reminds of when a classmate at school and I jerked off together. It was st a school party, we went into the theatre which was empty 'cause there wete no events planned in there, we went in the backstage part of the theatre and we jerked off together.