> The homes' 200-amp panels don't have enough spare capacity to add a charger. (3 old less-efficient HVAC units, pool pumps, hot tub, electric oven, clothes dryer, etc.)

200 amp is a LOT. You will do just fine if you manage the loads, just install a smart charger that can monitor the overall power use and cut the charging rate if the capacity is getting low.

My house is on 125 amp service, and I have plenty of high-power consumers. It worked for me!

TechnologyConnections has a great video about it: https://youtu.be/CVLLNjSLJTQ?t=793