VFDs supply current. Simply add up all of the motor currents (do not use HP) and purchase a single drive of at least that size. Check with the VFD manufacturer, it would be normal for them to require some type of load reactor/filter (maybe even one per motor).
Also each motor will require it's own overload protection.
All motors need to start at the same time, do not have the VFD "at speed" and then turn on motors. This is called "slamming" and requires more complicated sizing.
