We were flying to France and we'd bought Basic Economy, and we were ALL seated separately. Because our son was three at the time, they bumped some people so one of us could sit by him, but they were not happy about it, because they were splitting up other parties.

Since then, we only fly main, but given the size of your family, chances are you'd have at least 2-3 seats together anyway. I don't see them sitting all of you individually. So if you get some random seat off alone, the older kids could handle it.

You might consider buying basic for your kids who can handle sitting alone and main for those who can't.