Regular condoms don't fit. Never asked my Dad.
I had to trial and error before I realized that losing circulation was not a good thing. I didn't use condoms ever and still don't. Somehow at 24 and 50+ girls later, no kids. I have had a curable std once, god damn cheating whores. Anyway, once I realized when a condom fits and don't squeeze your dick to death, it isn't that bad, I've used em on whores in question.
Be honest with him, only thing you can do. If you lie or sugar coat it, he may never trust you again.
DO NOT TELL YOUR WIFE! This is man territory, she doesn't talk to you about her ovaries does she? Your son has trusted you with his dick. Keep that trust. Wife will just overreact and think her baby is to young.