You don't need dual chargers to use a HPWC. When it gets installed, it will be set for the maximum charge it can deliver based on the circuit wiring. If a Tesla with a single charger is hooked up to it, the car will only draw 40 or 48 amps of current (depending on when the car was built) even if the HPWC is installed on a 100 amp circuit (which permits 80 amps of charging). If you hook a car with dual chargers up to it, the car will draw the 80 amps and charge twice as fast.
If you install an HPWC on a 60 amp circuit, a car will either draw 40 or 48 amps depending on its configuration as the HPWC will not provide more than 48 amps of current.
Think of it this way -- while the HPWC is called a High Power Wall Charger, in fact it is not a wall charger...it is simply a plug with a certain amount of power available. The charger is built into the car and the car will draw the lesser of (a) the onboard charger's capacity or (b) what the circuit will allow.
This is why many people go with a simply a 14-50 outlet and use the universal connector cable -- especially when the price differential is so much compared to buying a HPWC. Now that the HPWC is down to $500 (for the 8 foot cable $500 for the 24 foot cable) the price differential compared to a second UMC cable is much less. In your case with a dual-charger equipped car, if you decide to install a HPWC, make sure your electrician installs it on a 100 amp circuit or you won't get all the charging speed your car can potentially get from a HPWC.
