I know you are not home currently, but maybe you can forward directions to caretakers .I went out this morning & checked on the kits, 10 of them had pretty full tummies, which I was very happy about. The other 3 looked like they managed to get some milk, but their tummies were a little wrinkly, so I tried to give them some more formula, I managed to get a little into them.
This is just a thought, and I'm not an expert by any means.
This is what I would try. I have tried this method with my baby pigeons to some success.
Remove the 10 or so littles, from the mamas teets, and place the 3 hungry ones into position. Often times the weaker ones are not able to get to the food, and it is a downward spiral at that point.
I'm not sure how many teets a rabbit has,

With my pigeons, when I seen one getting less crop milk than the other, I could see the larger growing like a BANDIT, while the other seemed to stall in growth.
I also know about natural selection theories, but you are trying to have as many of these babies survive, since you are willing to supplement their food. (formula)