Without a major re-wire, you won't be able to use all 3 at the same time....even then, the "normal" campground pedestal won't be able to supply the current. Most likely, neither will your generator. With few exceptions, everything is designed and wired for 2.
IMO, if it gets THAT hot...the simple solution just might be one or two fans to move the air around. Only once, with my motorhome, a heat wave in New York State, the temp was over 105. On generator, both my units were cranking fully, but most any a/c unit(s) can only cool like 15 degrees under the outside temperature. Even a house central air unit.
We were on the generator because the power at the campground went down (due to the heatwave)....brownout or complete stoppage....so we spent alot of time that day at the pool. And, as a sidebar, the generator and the a/c units performed flawlessly. But again, there's only so much they can do under such extreme heat.
