The youth advanced tickets can be purchased in advance. You can buy more than one as long as both people have ID's with them when they pick up the tickets.
"Love the Art in Yourself. Not Yourself in the Art." -- Stanislavski
Yes, I bought 2 youth advance tickets online and had no problem picking them up at the will call. They never asked for my or my friend's ID, but they probably don't unless you have the misfortune of looking prematurely 26.
Yeah, you can buy them online through the second stage site. On the first screen you just say how many seats you want and then the next one will let you choose if you want regular or youth tickets. No code needed and I think it's $29 per ticket with the fees.