[Byron]

I'm sure Abby must be aware that spoof letters often arrive but no doubt they meet a journalistic need to fill her page nevertheless, even if she suspects something.
(some agony aunts have been known to make up their own "readers' letters" anyway)
On the assumption that this is a genuine one I too can't understand the odd reply about the mother.

The age and upbringing of the father who writes here may be relevant - he seems to be overtly worried about some innocent and naive behaviour in the many facets of young male bonding which does not conform to the standards of his own youth. He has already checked on what might for him be most inappropriate sexual contact and he agrees every guy is having fun.
He just has to move with the times - has he never heard of what some young guys get up to in college fraternity initiations ? (probably far more for him to worry about there). Anyway if he is the head of the house HE should be making the rules about use of the shower under his roof and who gets invited to stay (sounds like a bit of a wimp to me).