It sounds like there’s no permanent damage done, so hopefully this has been an informative experience for both you and your family with rabbit care expectations. If your family may continue to contribute to your rabbit’s care, it is important to stress the importance of the correct diet; not only in content, but also in quantity.

The weight gain could be from excessive sugar from fruits, over-eating pellets, and/or inadequate exercise. Not having any hay for a week is… disastrous for a rabbit’s gut health, to my understanding, so that is worrisome.

Unless they are not eating for any reason, I would as quickly as possible transition to as much hay as possible, the proper amount of pellets, and eliminate treats for a while so their gut health and appetite can get back to normal. Also encourage exercise, so make sure they have plenty of free-roam time in a large space with traction so they can easily run around.

… And again, cannot stress enough the importance of educating and making sure caretakers are clearly understanding your directions. I am not putting all the fault on you, as it is also the caretaker’s responsibility to retain information and ask questions if unsure. The fact that hay wasn’t given for a week, when hay is the #1 most vital part of a rabbit’s diet and health management, is a major misstep in communication and education.

I would actually recommend a vet visit sometime in the future as well. Having an improper diet for that long can have health consequences beyond obesity.