This is difficult! I think they will be fine for a few days if they get pellets and greens, esp if they have some little bit of hay in their boxes. Greens are comparatively low in fiber, but they do provide hydration, which is also super important for tummy function.
I think its a good idea to give them greens more often now! I’d also divide their daily pellets up into several smaller servings and give them throughout the day. The rabbit GI tract is “designed” to get smallish amounts of food often and. I’d not give carrots or fruit or anything else that’s sugary these next few days, because their tums will be a bit vulnerable now until they get hay again.
If there’s still som hay in their litterboxes, maybe you could take a few pinches of it and put in tiny piles here and there around their area, to encourage them to eat it? “Found” hay is often more attractive to buns than served hay. (Yo obv want them to eat as much as possible of the little hay you have).
If you can get fresh pesticide free grass you could give a little bit of that, but this time of year fresh grass is v rich and full of simple carbs, so it’d have to be just a little bit. It’s not really a great option unless of course they’re very used to getting fresh grass.
Twigs like apple (pesticide free) or willow would be really great in this situation though, but might not be easy to source if you’re in a city.