2nd&3rd Router gets always gets disconnected from LAN

(a bit of intro)
So, I have this home setup, 1 router/modem (192.168.100.1) from my isp broadcasting at channel 6. 1 router (channel 11, 192.168.0.1) connected via cat5 on main router's lan1 and another router (channel 1, 192.168.0.1) connect to the main with a cat5 on lan3. all of them have DHCP enabled.

Now I have these 3 network groups that don't need to communicate with each other. I initially tried to make it access point mode or range extender mode. but the main router DHCP Server crashes. I can't connect the whole house to the main due to range issues. it is already placed in the middle of the house, but because of many concrete walls, I had to add other routers

(The Problem)
From time to time router 2 and 3, returns "Request timed out" from ping (connected via WLAN, also can't access the router homepage via local IP) then the those connected to it (via WLAN) will be disconnected and when i try to reconnect, it will "say cannot connect to network". But connecting to the main router(provided by ISP) it connects and has an internet connection. Any solutions or ways to detect the cause of the issue I'm having?