Since you don't want to use wiifi, all you really need is one with multiple ethernet ports.
Most common wi-fi routers have at least 4. But not all of them.
You need to know a few things about your computers. How fast is the wi-fi on them?
There are several different speeds. a, b, n, g, ac, and ax. Newer computers will have ac or ax.
You want a router that matches the wi-fi on your computers.
If you only want to use Ethernet, then the computer will have to be close to the router, or you'll need
long cat6 cables. ( maximum is 100 feet ). Most newer computer have gigE or faster, make sure the router
supports what ever speed your ethernet port is.
Edit: I just saw your last post. A router "routes" between two different subnets. It sounds like you don't need to do that.
All you need is a switch. A switch lets you have multiple computers on the same subnet.
Make sure the switch ports match the ethernet speed on your computers.