Well, we don't want to upgrade the connection with the utility, but would like to load the batteries of the cars without going over the available power. The aim is to have a stable load, maybe even to do demand response.
Car owners will pay for the electricity, and the counter is not the issue. The problem is really to adapt the charging power to the number of cars needing power.
Regarding Zappi, I don't think that 2 Zappi can communicate to share the available power. I have only seen a stand alone configuration.
On the long run, the aim would be to load the cars with the PV on the roof, but this is only in 15 years (or earlier if subsidies end sooner than expected).