Interesting.... You're right about not being able to run both A/Cs on 30amp service..... BUT..... My 1999 HR Endeavor is wired for 50amp service and runs everything on-board at the same time without hesitation on shore power. When running on the 5,500 Onan on-board genset it also will power both A/Cs at the same time, as well as the fridge on electric, microwave and electric water heater with plenty of power left for outlets to charge phones/computers and run a floor fan. Only thing we have to do when on genset power is turn off the water heater when we run a hairdryer.
You positive your Endeavor is only 30amps? There's not a 30amp adapter that got left on the end of your shore plug is it?