Editing: misread. You can wire a GE smart dimmer and add-on in your 3 way and a smart GE dimmer in the other switch and make SmartThings have the two switches work together. If you want a “fake” 4 way. Disadvantage is they will not turn off or on together (slight delay) but no new wiring is needed.
You can open your ceiling and run a two wire line between lights and disconnect your single switch. Still using SmartThings there will not be the flicker on/off but you will still experience a slight delay with the single switch.
Now here’s an interesting point, since GE add-on paddles are different than standard 4 way switches. You should be able to run a 2 wire line from either 3 way switch box to either the single switch or light (where the 2 line wire from the single switch goes) in your other set and make 4 way switches (1 GE Smart Dimmer, 2 addons). 4 wire lines are not needed. In fact you can add just one 3 wire line to get everything to work if you go from either 3 way box to the single switch light.
Give me a bit and I’ll attach a diagram