Agree that you need to pull all batteries. Label the coach battery wires and take pics, before removing. If there are any bulges, proceed directly to a battery or autoparts store and exchange for new batteries. If no bulges, follow the instructions above of charging for a couple days and then have an autoparts store check them. You will want to ensure that the batteries are off charge at least an hour before testing.
Does your converter require a battery inline to work? Most modern ones do not but you should post your MH make, model and year, as well as converter model. You should be able to disconnect the house batteries, plug into the genny and, if the converter is on and working, run the 12v devices (lights in your coach).
Have you thought that the 50A light has not come on because the system did not detect 50A? This does not mean that electricity is or is not passing through. Do some checking at the circuit box and lights in the coach. If electricity is getting to the circuit box, check to see if your converter is getting electricity and that is putting out 14+ volts.