What does your Ford Edge's owner's manual say about towing it 4 down?
Specifically, look for the section on recreational towing. Does it say that you need to disconnect the battery before towing it? Some Ford vehicles require that.
This sounds like you have one that requires you to disconnect the battery when flat towing, to prevent exactly what happened to you - transmission electronically shifting into gear while towing.
If that is the case (required to disconnect battery when towing and you did not), then Ford is right on here, and this is indeed your responsibility. This would not be the first time that has happened, either.
The other issues you had with brakes apparently dragging and doing some damage....Welll, that's a whol'e nother story, and shows why no matter what system you use, you need to wire in an indicator light of some kind so that you know in the Motorhome exactly when the towed vehicle's brakes are engaging or not. If you'd had that, there is a good chance you'd have known there was an issue before it did so much damage.