I had a group like that just last night. We spent a couple hours on Oryx at least and we were about to give up when we started doing well and finally managed to get it done. You just have to stick with it and not take no for an answer, and if people leave you make it clear that you'll keep going with whoever stays and then find other people to take the place of whoever left. Also keep your (and your team's) spirits up, be positive, correct people's mistakes nicely and keep saying "that was better, good progress, come on people we got this," or things to that effect. And if people say they need a smoke break let them have it, my team took a break for five minutes for a few people to smoke a cigarette (not me) and although I was afraid someone would quit, no one did and we got it done on our very next attempt. Just have faith that your team can do it, and as long as they're high enough level and don't give up then you shouldn't be disappointed. People jonesing for a cigarette aren't focused though, so if they say they need one let them have it.