Don't quote me, but i think the gala is open to all as long as you have formal dress. Though, i got the three day pass, so i don't know if that goes for all. In my honest opinion, I think just the polo and slacks should be good for your son. The blazer mixed with the polo may throw it off a bit. As for you, you should be okay as well, i dont believe it has to be a "ball" dress but something nice formal and clean to wear.