I would talk with your engine and alternator manufacturer and get a governor and regulator that will allow paralleling and load sharing.
Can you do it with a PLC - I suppose so
BUT
why take the time when engine governors and alternotor regulators have had this capability for decades. Why try to outdo the experts at it when they have forgotton more about it than most of us? The main hitch I see is getting the control signal to match an actuator in the governor and add a circuit to the regulator.
Even the antique units I ran on nuc submarine (69 to 73) had automatic regulator and governor (steam and diesel units) they could be paralleled and load shared - we ran split bus to avoid losing everything though.
Dan Bentler