Unfortunately the approaches may not be simple.

To just get access to the files on your desktop,
you could set up the desktop to act as an SSH server,
then you could just "shell in" from your laptop
and get to the files.

Or, samba shares could also be set up as well.

If I'm not mistaken, each machine will need
to have a static IP address assigned to it -
the software config (HTML) page inside your
router (if using a router) should be able to
reserve IP addresses to each machine once you
tell the router the MAC address of each machine.

As for printer sharing - if the printer has an
ethernet (RJ-45) connecter, then most likely it
can be set up as a network printer- again it will
need a non-changing (Static) IP address, and from
there I'm pretty sure you can just set up each
Ubuntu install to "add a network printer" and point
it at the printer name/IP address and in theory
you should be good to go.

Sorry I don't have exact "step by step" directions
here, but the above is at the least a good
"high-level" starting point.