Going back to the original question
You know what, I don't think I'd go via anywhere in the USA. 7 people, as others have said, is a lot of herding around. It will probably cost more and you may even need to travel to the airport the day before but I'd get to London and fly non-stop. Whatever the relative merits of BA and VS I suspect most people here would agree they are much better airlines than any of the US carriers and the hassle factor associated with changing at Detroit or Atlanta is eliminated.
I live in Somerset and went to Seattle this summer. I could have gone from Bristol via Newark on Continental but I went non stop on BA. Saved about 6 hours airport to airport, cost me more for the fare and because I went up the night before but it was a breeze (or as much of a breeze as any flying is these days).