[GraemeJ]

I'm not sure - someone would have to test that. I don't know if the device acting as the hotspot also participates/communicates on the network it creates.

I don't know either. Additionally, not all tablets accept SIM cards.  Looks like the BOOX tablets don't, by a quick scan of their website. 

However since someone is almost certainly (these days) to have a smartphone, that could be used as a hotspot with the tablets linked to it.