Need help creating wireless network across church campus

I'm trying to cover our church campus with wifi using 3 Airport Extremes for the main buildings and an Express for the 2nd floor. I also need a secure network and a guest network at each space.
Currently- the Extremes are each setup with an ethernet sending them Internet and they each have their own network but none of the guest networks work.
When I tried setting up the Express to extend the network of the nearest Extreme- it didn't work.

Any suggestions or help?

How are they all connected via Ethernet? Do they all feed back to the main extreme with the internet connected into its WAN port and then the other Extremes hook into the LAN ports?