The best place for the beginners in your group would be Beaver Creek. It's unique in that a large beginner area is actually at the top of the mountain rather than near the base, which is where a lot of resorts have their beginner areas. There are several trails reached from the Cinch chair lift (lift 8) or the slower double chair 5. Those who do not want to ski the cat track or intermediate trails back down to the village can download from mid-mountain via the Centennial express lift (lift 6). Those who want to ski back down would probably find Gold Dust easier than Latigo, which has a steep pitch in one section. Your intermediates would benefit from the free mountain tour that starts at the top of the Centennial lift. Gives them an awesome experience of the resort that would be difficult to cover on your own not knowing the mountain. They go at about 10 a.m., I think.
At Breckenridge: The low-intermediate in my group has always enjoyed Springmeier and the beginner trails it feeds into on Peak 8. Yes, Peak 7 is full of nice intermediate trails. Note that the trail on the far side , Monte Cristo, is the least challenging. The trails get steeper as you move toward the center of the trail map. My low-intermediate will only ski Monte Cristo.
Vail? I love Vail, but I don't think a true beginner or low-intermediate will enjoy it. The intermediates will enjoy the trails from the Mountain Top express lift #4 -- Espresso, Cappucino, Swingsville and Ramshorn on the other side of the lift. Hunky Dory from the Wildwood lift is cool. These trails get sketchy at the bottom and the base of both lifts is very close together so it's a bit confusing at first.
I would focus on Beaver Creek with the group you have. It's a great time!