Every access point on the same channel (as well as every client) shares bandwidth. If all of the networking is happening on channel one, with two clients, you would end up with 1/6 the bandwidth. The problem isn't interference, it's making a 6 lane highway a two lane road.

If you use distinct, but overlapping channels, you end up with radio level interference, so not shared bandwidth, but lots of retransmits when both are active.

The best case is using the non overlapping channels which allows you full bandwidth and very low interference.

So I would have your backbone on some far channel from your clients, or your chatty mesh protocol will slow the normal clients to a crawl. You could even use the three distinct channels so that one is backbone and the other two are not overlapping where the two circles fall in the same territory.