Is there a known issue with MacBooks and bluetooth occasionally restarting?
It's anecdotal, but I have never experienced such an issue on any of my Macs. I haven't heard others complain about it either.
As far as I understand, you're saying that Bluetooth stops working for a few minutes every once in a while - even with only a keyboard and a mouse connected - and it happens often enough that you're impacted even within a single conference calls.
I would try using wired devices and only having a single Bluetooth connected device. Try different combinations to see if you can single out a faulty device.
If that doesn't help, try going to other locations and see if the problems goes away. You might be dealing with interference from a noise source, which have affected all 3 Macs in the same way.