How to install an Insteon switch on a multi-way circuit
Insteon is very simple to install.  

The concept of 3-way, 4-way, or multi switch circuits doesn’t exist in the traditional “wired” sense.  

Use the 2466 in the last switch position before the load.  The red wire from the switch goes to the load.  

Now you can use additional 2466’s (or many other insteon devices) at the other locations.  Basically the 2466 needs hot, neutral and ground.   In these other locations you cap the red wire on the switch because the switch isn’t actually switching a load.  Don’t have a hot and neutral at the switch location?  You re-wire the circuit to make it happen for your case.  You had 2 travelers before, you re-wire the circuit to make those old travelers hots and neutrals.

Now to get your multiway switching to work you utilize the insteon linking process.  This is best done thru your hub, but there is also a painstaking manual linking process described in insteon manuals.  Hint: if done thru a hub: for straight multi-way switching add each device individually to the hub, then create a scene and add all the devices as a “controller”.  (A controller is also a responder, and in a standard multi-way switching scene every device should be a “controller” and no device should be classified as “responder”)

(Disclaimer: the only two non-insteon switches in my house are both garbage disposal switches.  I've encountered every wiring possibility at some point. If you need more info ask away and I'll edit)