One note on using the Generator, particularly on a diesel. Some have a cutout circuit to block the house charging system from supplying power to the engine batteries when the ignition switch is on. In this case you need to keep the aux/emergency start button depressed. So just starting the generator may not do the trick by itself.
Since the op's generator would not start he could have used one jumper cable to combine his batteries long enough to start the gen. Not the safest thing to do because at that stage there probably would have been a good spark and that is not good. Turning off the battery disconnect switches would probably suffice while connecting the cables.
So if you notice something like this get the generator fired up early on.