|You have to connect all three to a router or a layer 3 switch. This way you can have three different subnets on the "wan" side of the router and one lan segment all in the same subnet.|
Or, if you have the ability and access, you set all three routers lan segments to the same subnet. This gets complicated. Here's why;
1. you have three gateways
2. you have the potencial of three dhcp servers
Easiest thing to do is the following;
Disable all dhcp servers
Statically assign gateway and ip to the workstations/network devices.
Set the routers as follows;
All routers should go into a switch [managed preferred]
From there they go to the printers/pcs. Some you would point to gateway 1, some to gateway 2 and some to gateway 3. You are doing a manual load balancing.