Yes, it is possible to start multiple motors from a single soft-start. Typically, the motors are started sequentially and are identically rated. In a typical MV application, additional contactor cabinets are connected and control-tied to the soft-start. Once the first motor comes up to speed, the soft-start “Switches” to control the next motor in the sequence.
In the case of only two motors, some soft-starts are manufactured with dual settings to permit starting of motors that have different starting characteristics, but actual motor output during ramp-up may not differ much, being limited by the inherent performance characteristics of the soft-start.
Multiple simultaneous starting of motors requires that the motors be identical and that the soft-start be sized for the total load and supplied with supplemental cooling.