M.P.
I don't know this kid so it is hard to tell...but is he being a little beligerant of bratty here about the restaurant? Why does he want this place so badly for the party. Have you tried saying to him that you guys are going to take him to dinner there yourselves right b/f or after graduation? B/C from where I am standing while yes, he IS the graduate, he is sounding a little like gradzilla here. You guys just can't afford the party of his dreams. period. Tell him yeah-you would love it if you could but you are just not in the situation to take 20 people out to eat. Honestly-many people would find it a hardship. And at least around here home parties are more fun anyhow.
So sorry T.-I know how hard you are trying here but I really don't like your app/cake at restaurant and go back for burgers. Not really tacky-just a little disjointed and doesn't really make sense. And it will still be pricey b/c of course everyone will order drinks. And one more thing-your older relatives will much prefer your house over a pub I would think.