I can't find other devices on my network.

I am using a WNDR3700x2 router, with a wireless extender on another floor. When I log into the router itself, I can see all of our devices, both wired and wireless. I also downloaded the netgear genie app, and they show up there, too. The problem is that my devices cannot communicate with one another, and aren't found when I display the networks on the devices themselves. All computers are running Win 10, and both wired and wireless access to the internet works great. Through file and printer sharing, I have managed to get one wireless laptop to talk to a desktop computer, but only by making the desktop wireless, also. Files can now be accessed by both computers, but the laptop does not see the printer that is hard wired to the desktop computer. (Before Windows 10, the wireless computer could talk to that other computer when it was hardwired - that no longer works.) I am also unable to see either the wireless laptop or desktop computers from a different wired computer.

I think I am being stupid here, but am tired of hitting my head against the wall.... I read another post about this, where the gal had to reboot her router every morning for her computers to see one another. This is not the case in my issue; rebooting doesn't change anything, and the router login shows all devices connected - I just can get them to see each other through the computers.