You'll most likely need an invite for you as well as your guest. They take the invites from you when you enter so not likely you'll be able to get both into different lounges. There is a pay option at the Jazz Lounge. I've seen a guy paying when I've checked in before and he did get a receipt so I'm guessing there's a legit way to do it and then the more common way of doing things in this great land.

The commoner area is really not bad at all. Wifi and coffee shops are a plenty.

I have been able on occasion to get Delta to give me two invites to bring colleagues in. You might try asking. I've been told no and I've been told yes. Can't hurt.