Battery disconnect Switch

Okay, thanks for all your replies, this is what we know now and where we're at. The meter showed the chassis battery at 8, two house batteries were at 9 & 0. We jump started the chassis battery and started the engine, let it run for 35 minutes, still no power inside or to start the generator. Checked the chassis batteries again with the meter and there was no change. The batteries will need to be replaced, but should I still check the switch? Wouldn't it show dead if there's no power from the batteries? Again, thank you both for your replies, I kinda fly by the seat of my pants, knowing a little, but need reassurance that I'm trying the right things since this is our first MH, we've had a tt & toy hauler in the past. Oh, and I turned the engine off and it started right back up, I will try it again tomorrow to make sure that battery is still good.