We're a 2-teacher household 2 computers bought at the same time trying to do distance teaching. 1 streams videos to kids; the other doesn't?

Ok, thanks for adding more info!

A few areas of concern come to mind:

1. What sort of video cards does each machine have and how are they different?

     Are you confident enough with tech to swap video cards between systems? (You'd also need to install the driver for that card, too.)

2. Are both systems using Ethernet or Wi-Fi? If Wi-Fi, what differences do the Wi-Fi cards have? (Also, if using Wi-Fi, try to test at least once using Ethernet.)

3. What's running on each computer *before* running Google Classroom? In other words, "What's booting up with each system?"

4. Are both machines running an antivirus app and is it the same one? 

5. Are other teachers having a similar issue?

I'll admit that you have a tough one to solve. We can only tell you what we'd try in your place. But since your issue seems to revolve around video... I'd see what happens if I swapped cards. Did the "problem" follow the card?  If yes, then that video card should be replaced with one like the "good one" or better.

Good luck! 👍

what do you mean by doesn't stream

do you mean you get an error or bad quality of the application won't start

assuming they are both wifi what are the network cards

one could be faster network connection than the other

try to provide more detail