Help resolve IP Address Conflict & set Static IP (Network Crashing Daily)

Hello Friends,

Could someone help me figure out how to set static IP addresses in an attempt to resolve my network crashing problem? I have a few questions on how to set things up.

1) Do I need to set static IPs for the devices (phones, laptops, etc) on the network; or just the routers? Or all of them?

2) There's an IP reservation menu in the EERO app. It makes it very easy to reserve the IP address for normal devices, but it doesn't list the routers as something I can reserve an IP address for. There is a way to add reservations manually. It requires me to input an IP address and a MAC address. While there was only one IP address; when I checked the MAC address details for the routers, I saw 4 to 5 different MAC addresses per router depending on the model (2 for ports, 3 for WiFi? Screenshot attached). Does this mean I need to add 5 reservations per router to make it "static"?

3) Is there any way to confirm that this is in fact an IP address conflict that is causing the network to crash?

Problem:

Based on what I've been reading, it's most likely an IP address conflict? We have a large network for a household, and the network dropouts daily, about every 8 to 12 hours (if not more). The entire network crashes and I can see that the routers/extenders keep attempting to reconnect, but never do. They just end up on a loop of crashing and attempting to reconnect. This is usually remedied by switching off the main router and network switch, waiting a while, then switching them back on.

Network Setup:

18 Eero devices in total due to brick construction. Signal wouldn't reach any other way. You can check the network diagram using this link. The signal goes from the ISP ONT box to the main router, which is followed by an unmanaged network switch. From there, the switch takes the signal via cable to multiple routers distributed in different locations. Everything is connected via CAT6 cables, with the exception of 3 wireless extenders. There are roughly 50 to 60 devices connected to the network, that's including all the "smart devices", lights, etc. A few more if people come over.

Past attempts at solving:
 

EERO support was so basic and no help (replaced devices, bought preferred network switch, etc.)

ISP replaced ONT box and made sure everything up to the ONT box from their side is ok several times

Replaced all cables, sockets, etc. Everything is CAT6 and shielded.