If you have good fresh kale and parsley, those should last a week. I’ve often had both of those to last almost 2 weeks if they are fresh.
In addition to writing down the basic care info for your Grandma, is it possible that she can come over beforehand and observe your feeding and care of them? She could also get to know them and make sure that they are comfortable with her. Will they have to be caged or penned the whole time, or can she let them out for exercise? If so, will she be able to get them back into an enclosure (if you use one)? By observing them for a while before you leave, that would also give her an idea of normal rabbit behavior and what would or would not be a cause for concern.
She will need the name and phone number of your vet, as well as the name of an emergency clinic if there is one nearby. I don’t know if you keep a medicine kit with some basic supplies or not. Would your Grandma feel comfortable with giving them any kind of treatment if needed? You could discuss that with her.