I have the same set up. I don't have any shared wiring.

Do you have two 24 volt transformers? Perhaps the installer is only using one transformer for both systems.

Are the two systems using a common return?

Mike-24 Volt Transformer don't know what that is-or what to check to answer that question..but is that ok if that is going to be their explanation I have a call into them now? Plus I think the wifi has been a problem server always seem to be down have u experienced the same?

I take back my earlier idea. I looked at my installation closely to satisfy my curiosity. It turns out my Infinity furnaces have built in 24 volt transformers. I assume yours also has this feature.

The thermostat runs off a 24 volt supply. Usually it is mounted externally.

My Infinity controllers are 4 years old and do not have Wifi.

My only thinking is the installer wants the furnaces to communicate with each other. That is why I was asking if you have a common return. Have you seen both systems operate at the same time?

Don't quite understand their explanation- seems "extra " wires something to do with thermostat I believe so instead of "pulling" a wire they connected them to the other unit ..however I have requested they "pull new line because I don't want them together..they have agreed.. See photo any thoughts thanks

I'm guessing your referring to the set of metal-clad aluminum cables that are running out of the condenser. Normally MC is used for 120-240 volt circuits so they may be sharing the same circuit to feed both units however this poses several other questions. Do you have a disconnect mounted next to the condensers to shut power off to them? MC cable is not permitted for use outside- you should have liquid tight flexible conduit or Carlon as it is commonly referred too, run from a disconnect which is then from inside, then from the disconnect-out the bottom with a loop down and then back up into bottom of conndenser. Last but not least the MC cable is available in multiple sizes but is normally #12 awg, which is sized for a 2-pole 20 amp breaker. I believe if it were #10 the aluminum jacket would be a different color and would be suitable for a 2-pole 30 amp breaker.
I apologize if I was completely wrong about the setup you have, just to trying to help out with what I noticed. Good luck.