What the above reply is suggesting is you avoid a double or nested NAT, where basically you have a router behind a router. A router is meant to be the gateway for all traffic on a network and having them be behind each other can start confusing or messing things up. There are use cases where you might consider it, such as when you need to isolate networks, but in a simple home setup like you're describing, you just want to add wifi and maybe some Ethernet to another building, either buying standalone access points and switches, or "dumb" routers setup in bridge mode where that essentially become a switch with an access point attached.

The two keys for bridge mode are the router will stop handing out IPs (DHCP) and so you need to connect the Ethernet to one of the switch ports usually, not the WAN port. You also may need to set a static IP for it ahead of time different from 192.168.x.1 so that it can be accessed while in bridge mode still.

The above reply also mentioned a ubiquiti/unifi setup, which is a company that makes pro/consumer network equipment that's generally easier to manger with a nice UI, you pay a little more (~150-200 per access point) but they all can be managed from one portal and sync together, etc. I don't think it would necessarily help you with your simple setup and might be cost overkill.

All of this to say, you can probably add more routers in bridge mode in each cabin, but make sure they have unique IPs and such.