@John_Tucker in a 4-way (or 5- 6- 7- whatever-way), there's a 3-way switch at the line side, a 3-way switch at the load side, and one or more 4-way switches between the two. 

You really only need to replace one of the 3-way switches, preferably the line-side switch, with a smart switch. This will "smartify" the whole thing. The reason tp-link recommends replacing both 3-way switches is for aesthetics and more reliable sensing of the on/off state. The reason multi-way setups often don't work is because we're driving low-current capacitive loads (primarily LEDs), and the longer length traveler wires create an additional capacitance issue. This throws off the Kasa switch's current-sensing capability, usually resulting in the switch showing the lights as being off regardless of their actual state.

The simple fix is to install a 1MΩ resistor (like one of these: https://www.amazon.com/dp/B08QRF4DM7 ) between the traveler terminals of the Kasa switch. In most cases, this will "bleed off" the capacitance between the travelers and allow the switch to accurately detect current flow.