Home network setup problem


I have spent several hours trying to network my 3 home computers. I have my Main computer, my wife's computer and a Laptop. I have enabled file and print sharing on all 3. I disabled password protector on all 3. Private network on all 3. My main computer sees laptop, my laptop sees main but asked for cridincials, which I don't know what cridincials it wants. And my wife's computer sees main but says there is an error when I click on main. My main reason to network is so I can print from all three to printer connected to main. It is not wireless but connects by USB.Running Windows 10 Pro 2004 all  3. Any suggestions on what I might be doing wrong.