|Go to the properties of each printer, make sure they are shared. File and printer sharing must be enabled. Add exceptions to any and all firewalls in question.|
To test the shares, go to machine #4 and click start, run, put in the IP of the #1 machine.
\\192.168.0.100 or whatever it is and press enter. You should see the shared printer.
If you do, open the printer folder on #4, click add printer and go through the wizard or sometimes you can actually drag and drop the printer from one machine to the other.
Do the same on all machines with all printers.