Bob, if those guys were wearing hell's angels jackets, then no. If the guys and gals are spooning, no. But as you put it:
"The girls didn't look too interested in them..."
Why not befriend the guys AND gals and find out the score? No need to ask directly, but either the guys or gals might drop a hint as to whether they're coupled up or not. If they are, you can eject and open up another set elsewhere. I'm in the middle of bootcamp, and a couple of times, I've started up convo's with a girl when her guy was seated right next to her or to me. When it was her boyfriend, he gave me a quick, polite, but definite hint that she was taken so that I could eject without losing face, and without him escalating into a more confrontational stance. Also, if you see the girl avoiding eye contact and deferring to the guy you suspect of being a boyfriend when you talk to her, that's another hint that she's taken.
But, you never know until you approach.
If they're NOT coupled up (that is, the male turns out to be a gay friend, or some loser she dragged along so she wouldn't have to go out alone, etc. etc.), hey...that's the situation you were looking for in the first place right?
Good luck with round two and post a field report.
PS: were these girls sitting across from the guys on the couch the ONLY pretty girls in the entire joint? Seems like you shoulda opened up some more sets, or at least looked around for more targets, unless it was a very, very slow night at this particular bar.
PS2: a while back, I was at a bar in the midwest and had one drink too many. I saw a girl who looked reasonably attractive and chatted her up for about 5 minutes. She was friendly, but seemed a little uncomfortable with the situation. Standing to my side was a guy with a drink in his hand, patiently watching us both with a shy, embarrassed grin. After I gave up on her, I started talking to my friends again. I turned back to look at the girl, and the guy who had been watching us was all over the girl, hugging her, kissing her, laughing, and so on. Yup, her boyfriend was polite enough to wait for me to finish with my set! This was a bar in a friendly midwestern college town though, so I don't recommend you try this just anywhere.