When you link multiple Roku devices to a single Roku account, the channels and purchases will be the same on each device. This is true for me. I have one Roku TV in my bedroom and a Samsung TV with a Roku Ultra connected in the living room. With one account everything shows up on both tvs. So here is my question......
If I hook up an antenna to my "Roku TV", will those ota antenna channels show up on my other "Roku Ulta Samsung Tv" or will I have to buy an airplay for the roku?
No, there's no way to get OTA channels from a Roku TV to another Roku device.
Assuming you don’t have cable anymore, If you had a coaxial hub wherever your cable came into your house AND have home runs to all of your tv locations, I think you could run your OTA antenna to the connector that your old cable source was plugged in and it should feed all of your sets.