Two air handlers one compressor

I recently purchased an 80's apartment converted to condo. Two story with separate air handlers up and down. They each have a thermostat and are not connected together in any way other than using the same compressor for ac. As you can imagine this has issues and needs help. It seems likely it used to be some sort of master/slave electrically and for whatever reason was converted to this. I called a couple local hvac places and they don't seem like they really want to get involved.

I'm looking for some guidance on where to point a contractor to resolve this.

source https://hvac-talk.com/vbb/threads/2242821-Two-air-handlers-one-compressor?goto=newpost