Oh my, what a tragic story. It is so strange to hear that the babies were following the mother. Usually the mother keeps them hidden somewhere, unless something disturbed their nest. What happened to the other babies? If they ran away, you should let animal care and control know.
The vet should have at least offered you some advice until you could see him/her. And I'm surprised they didn't try to get you in sooner.
I can offer you what the House Rabbit Society suggests: House Rabbit Society - Orphaned bunnies
Be sure to scroll for the suggested feedings for your bunny's age.
It is very nice of you to care for this bunny. I so hope this bunny survives and there is a happy ending. Please keep us updated.