can two desktops be connected to one router and only one modem?

[kindthing]

I have two desktops and only onemodem connection in the house and only one modem

 

[USAFRet]

I have two desktops and only onemodem connection in the house and only one modem

Yes. The modem sees only one device, the router. Whatever happens after that is all on you.
ISP -> modem -> router -> multiple devices.

Currently, I have about a dozen devices connected to one router at home Most wired, some wireless,