"Io e lui vogliamo una birra."
I think your last two sentences disagree with each other, Karen. :) I'm not a native speaker, but I'd guess that the reason why it doesn't accept "would like" is precisely because it does mean something different... it means something more polite than "voglio." If I wanted to say "I would like a coffee" when ordering a drink in Italian, I'd say "vorrei un caffè," not "voglio un caffè." Using voglio here could be considered overly familiar or rude (just as "I want a coffee" can sound demanding in English). I am guessing Duolingo will introduce the "vorrei..." construction later, but at the present time, it probably doesn't want to trick you into thinking you're being more polite than you are.