A new motor home with a good rust-free 5000 pound hitch & framework is questionable towing a full size cargo van loaded up. A 1977 dodge chassis motor home doing the pulling is alarming. You will need to determine if the hitch and frame of that old motor home can handle so much weight. It likely could not handle more than 3500 pounds if it were rust free. But given the age and likely condition, it might not be safe to tow anything at all.
Regarding tow brakes, that will be a sure requirement, and an expensive one.
I would rather tow the 1977 motor home behind the right rental truck before doing as is the question. If what you do is considered unsafe and you get into a serious accident with injuries or worse, you would likely be sued until you have nothing left but a lifetime of debt.
I agree it's wise to drive the van and motor home independently using two drivers.