I'd be shocked to see that lineup. I'd probably list Green as the team's 4th option at left guard. Behind Cooper, Bell, and Cleary.
I don't know. I was impressed with Green at tackle when he stepped in, while right now, Cooper is a guy who hasn't panned out and is on his fourth team with Arizona trading him after two years after making him a first round pick, New England cutting him after a year despite trading for him and Cleveland not even keeping him around for a year; Bell's on his third team primarily because he's been bad at tackle, but he did look better at guard; and I doubt Cleary's really much of a consideration and is on his fourth team after only sniffing rosters in his other stops.
The main thing hampering Green is his health, but his career so far has less warts than the others. I wouldn't be surprised by any of them, though, except Cleary.
I also think Green and Cleary getting time at guard with the starters is telling. Both are tackle backups so technically they don't need the position flex to play guard since we'll take both a tackle backup and interior (guard/center) backup to games. IMO, this means Dallas wants a look at them inside for starting guard consideration. The team clearly isn't looking at Cooper to start at center, so him getting time there also means IMO that Dallas is keeping its options open that he might end up as a backup. If Bell hasn't spent any time at guard, which we don't know but seems to be the indication, then I can't say the team is considering him there.
Still, it's very early and the position will get sorted out in camp. It could end up for all we know with Collins back at guard.