Depending on circumstances, I do this with just our dolly and our 38' MH when we have back-in sites although sometimes it's just faster and easier to disconnect the dolly and put them in the site separately, then reconnect. It's really just like any other trailer, the only problem is that the tail of the vehicle has a lot more swing than smaller tow vehicles, so it's really easy to jackknife it if you're going too fast and not paying close attention.
When you add the car too, while clearly not impossible that looks like you're just asking for problems as there are too many pivot points to keep track of and adjust for. That said I have backed the full combo (MH+dolly+car) a few feet on occasion, such as overshooting the gas pump, but not this far. If you came in straight, it should back up straight maybe 10 feet or so before enough error creeps in and starts to swing the car or dolly enough to make a difference.
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