Howdy All ! I am helping out at a local church and they have 2 Trane xe90
furnances that have two thermostats. The units are side by side use the same cold air and use the same downflow for out put. I understand they can be twinned to run on one thermo, PS I helped install theses units a few years ago , so I feel i can twin them give the correct part/info. Not to say I'm any kind of HVAC pro. I had a pro do the silver solderin and charging of the coolant lines way back when.
What you need is referred to as a twinning Kit. I want to forewarn you though that not all furnaces are twinning capable if hooked to the same ductwork. Check with your local equipment distributor to make sure the furnaces are twinning capable and they will give you pricing for the twinning kits.