Are my two early 2015 Mac Air's different from each other? Both the Mac Air's are early 2015 models. One has High Sierra installed and the other has Catalina. I see Hyper Threading is missing in the High Sierra version and the text Dual Core is missing even though it has two cores. Are these two different processors? Which one is inferior?
They are the same.  The marketing name of the Intel CPU is something they put in &quot;manually;&quot; it's not queried from the CPU directly.
I wrote a post a while back on getting the CPU architecture where I make note of this:
How do I identify which CPU a MacBook uses?
You can get the &quot;marketing brand string&quot; but then you'll have to go look up that information from Intel's website.  If you use the command:
sysctl -n machdep.cpu.brand_string 

You should get a string back that contains:  i5-5250U (I don't have a 2015 MacBook Air to run it on for the exact string).  That CPU was used on the Early 2015 MacBook Air on both the 11&quot; and 13&quot; models.
As for Hyper threading, it is fully supported on the i5-5250U CPU and see How do I enable Intel Virtualization in a MacBook Pro? for additional details on how to check for Virtualization support.