There is only ONE way to wire three way switches
Come on now plumber. You know he meant 3 way
circuits.
The first thing to understand is how your system is wired. You will need to take the switches out and do some simple testing. Details depend on how it's wired.
The next thing to understand is how the 4ways work, along with the 3 ways.
The 3 way circuit uses
two traveler wires, sending power on to one or the other of them. The 4way switch simply flips the traveler connections.
You 3way/4way system will have a 3way sw on each end and as many 4ways as you desire in between.
Pull out the switches and see what you have in there. A diagram will be necessary, or at least an accurate written description.
EDIT: IF you existing circuit is not wired thru the lights, all you really need is access to the
three wire cable running
between the switches. If you can cut that cable and splice onto it, you are good.
Cut the cable and, in a jbox, splice on to a new 3 wire cable and run it to the first 4way, Run the 3 wire cable to the next 4 way, Run the 3 wire cable back to other end of where you cut the cable.
The exact make up of the wiring depends on what colors the original installer used.