I need two computers to share everything

[Enquiries]

I'm upgrading my internet radio station computers. I bought 2 Window 11 computers, 1 for the main & 1 for backup. But, they don't talk to each other. I need someone working on 1 to see what someone working on 2 has done. I also need it so that if computer 1 stops, then computer 2 can continue putting the music on air. The computers are currently attached to the internet route via ethernet cables (they don't have WIFI). There are no more ethernet ports on the computers, so can't use an ethernet cross over cable. All of the ports on my router are in use (one to a splitter that I have both computers plugged into.) How can I get these 2 computers working together? I’ll need a printer added eventually, too. I'm not tech savvy so will need very simple instructions on how to make these work together, or happy to pay someone to come do it for me. Thanks.