Looks like you're doing your diversification calculations wrong by doing completely separate calcs for the combined garage and trailer feeder. Combine the loads prior to diversification as they are all on same service. This will lower your overall demand, because of the diversification.
Seems you're making this a little over convoluted. 340.40 Exception 2 allows 2 service feeders to one location supplying 2 meters with disconnecting means at the pedestal. From there, first trailer near pedestal not a problem as it is within the 30ft line of site. Second feed goes to garage and trailer, again no problem just need the 4 conductor from the pedestal to the garage (required for any sub panel feed). At garage just need to add a 100A Disconnect inline on exterior between the garage and the trailer within the 30ft line of site limits. No need for a neutral disconnecting type switch. Also, don't see an issue with the trailer disconnect being on the side of the garage (would meet code).
Simplest (and cheapest) way of load management for a gen set is with load shedding units, and no more space requirement as doing a "critical load panel, and no convoluted wiring back and forth from garage to trailer and back. Add the ATS at the garage main panel (as normal) and then feed through for the Trailer disconnect. The Load shedding units (load management) I've used monitor the individual load and the gen load and you choose priority of the individual load shed sequence. The self contained units I've used will control up to four 20-100A loads. and dry contacts for HVAC if you want to control that way. They also have expandable pack that will allow larger load quantities.
So say your priority is likely heat (non-shedding) - water - lights - cooking and last EV or laundry. It can be programmed that you determine the priority of load shedding, and it could be set so that "if" there is enough available power the EV charger may even be allowed without shedding and if loads increase it then will shed. Can be set as a permanent lock out when on Gen or monitored lockout that will restore if overall loads drop below established set point.