I have not yet had it happen that one of the packs lacks an alpha, so I have not tested this personally, but there's an option built into the hangouts which allows a pack member to claim alpha status if a pack currently has no alpha. If the dad becomes alpha by this method, assuming it works as it should, he will be able to invite his son into the pack with no trials needed. (He can also invite any other sim to become a friend of the pack, whether or not they are a werewolf, which is not a bad idea when it comes to non-werewolf spouses.)
One thing I did find out recently is that a teenager can become the alpha of a pack, even if the current alpha is an adult. While they cannot spar for it, due to age restrictions on that, they can still engage in an epic tug of war over it.
When it comes to the Wildfangs, teenagers have an enormous advantage as pack members, as skill gained while attending high school during active play causes rank to increase VERY quickly. Apparently, despite being renegades, the Wildfangs strongly approve of education and school attendance.