What distances are you working with?
Legitimate Ethernet cables should work up to 100 meters without need for extension.
Cables should be Cat 5e, round, pure copper, UTP 22-24 AWG. (No aluminum, or copper-clad aluminum.)
I will add the suggestion that you focus on getting one (the first) camera up and running and use that experience as a template for the remaining cameras.
Connect the additional cameras one by one and verify that all other connected cameras are working before adding the next camera. Easier to troubleshoot if only "one thing at a time" is changed.
Sketch out a plan showing all cameras, routers as APs' (if necessary) and then install cameras one by one following your sketch.
Keep the installation methodical and orderly.
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Yes: disable DHCP on any routers being used as an AP.
However, I would assign a fixed (Static) IP to each camera via the main router and the camera's mac.
Use some specific range of IP addresses to make it easier to identify IP addresses that are cameras.
Static IPs will avoid future IP address conflicts and help troubleshoot network problems.