David wrote:
At what point does it become infeasible to charge multiple cars overnight
using a single 80 or 100 Amp 2 phase supply?

I think it depends on the usage. It's doubtful that all family members are
going to be doing 300 mile trips every day, so need a full recharge of a
flat battery. A lot of those cars are going to do 50 miles a day, and at
about 4-5 miles per kWh that's only 10-12kWh needed to recharge. Assuming
the cars are plugged into the same charger, it can decide to prioritise them
based on who needs charging first, and then sequence them as they each
become full.

If it's a new build estate it would make sense to install 3-phase anyway,
though, given the extra cost is likely to be small.

(it is ever a thing to have dynamic load balancing across phases - where the
supply company can switch over your single-phase loads to a different phase
to keep the network in balance?)

Theo