They overlap hugely. That is the idea. They have the alternatives for each listener when they want to listen to something different, and the average listener uses up to 6 station per week.
They target young, middle and older women in 18-54, but also they target moods for women who will use two or even three of the stations.
And, as music and even market moods have cycles, when one goes up, another is flat and the other may go down but the average is always about the same.
For the advertiser, all they have to do in LA is add one Black/Latino rhythmic station and as couple of Spanish stations and they have women pretty solidly covered. f
The problem is that those are all older demos and at least one focuses on rock, a declining target.
Look at demos. Where do they have the least strength? 18-34? 30-49? 40-54? Men? Women? Where they need a demographic fill in, that is where the format will land.