How to Screen Extend Across Multiple Devices

Greetings:

I'm tirelessly trying to figure out how to extend my screen across multiple Apple products (the term I might mean, though, is dual-monitor although I think you get what I'm trying to do).

I have a brand new Macbook Pro, I have a brand new Macbook Air, and I have a 2017 iMac. Id VERY much like to use my iMac as a monitor that displays my newer MacBook(s) since they have greater processing speeds, my data, etc.

I keep getting told that this can't be done, but I'm having a hard time believing that Apple products don't talk to each other in that way. I'm hoping you forum people can really help me out. I'm even open to buying new cords, a third party app, or whatever is needed.

I wish I could simply AirPlay my MacBook device to my iMac screen.

Whatcha got, forums?

Thanks,

Cody