Your Fluke has already blown it's amperage fuses when you directly connected to a draw greater than 10.5 amps. No idea about the measurement you have.
Here's what I'd suggest first: Make sure your solid state BIRD is functional. One way to test this is to measure voltage at the starting battery and then measure voltage at the coach batteries. Push the "aux" jumper button that connects them and see if the voltage rises in the lesser battery.
Next, I'd completely disconnect that BIRD and try to start the vehicle with just the starting battery. Measure it to make sure it has a good charge before start initiation. If it's low (likely), put a charger on it.
You have a couple of problems---a battery interference because of a drain, a vehicle that hasn't seen constant use and may suffer from all the ills that entails (fuel system clogging, bad gas, ignition components not serviced, etc).
I'm kind of amazed that you seem frustrated about starting this vehicle. You may not have any experience with vehicles that are stored for a stretch but, for me, it is always a drama of covering many steps to get them functional again.
