[otnt]

It says I need to confirm that a passkey appears on master tablet.  Don't see this and don't know where to look for it.

I would remove previous pairings from Chrome OS Bluetooth settings.

Then as Mike said before:
"First, try to connect the devices in the system bluetooth settings. You need to make sure one of the devices is discoverable, and then from the other device, you must pair with the other device."

So once you trigger 120 seconds visibility go to Chrome OS Bluetooth settings and pair your tablets.
Then you can follow by connecting tablets in MS Pro.