Do your son and his close buddies have a go to beer? Get that for sure if so. I'd also ask the place your buying kegs from, they can give you good solid info. Buy 1 more of the main and one more of the full flavor than you think you'll need. Also, can likely return untapped as long as they are kept cold

"Life is not a journey to the grave with the intention of arriving safely in a well preserved body, but rather to skid in broadside, used up, worn out, bottle of Jim Beam in one hand and a .45 in the other, loudly proclaiming WOW-- What a Ride!"