Regarding question 2, the generator needs 12V power in to operate; the battery provide excitation power for the field (and to run the generator controls). If it's not getting enough power or detects any of various other problems, it shuts down. Many of the fault checks are disabled while the start switch is held in.
If this is a motorhome, you probably could have started the main engine so that the alternator charges the house battery and whatever battery isolator system you have engages, and then started the generator. Once it is running and the converter providing 12V power, it likely would have enough voltage to keep going and operating (and you could then shut down the main engine).