True 50 amp service is actually 100 amps total. Three AC units should be able to run, along with other appliances IF all three AC units are NOT wired to one leg of the 50 amp input. If all three are wired to one leg on the incoming service, than 50 amp is the limit on the AC units, but that should not affect the other appliances on the other 50 amp leg of service.
Of course if all of the AC units are wired on one leg and that leg trips on the park pedestal, it will shut off both legs since the breaker is tied together.
