My vet would have never dewormed (can't tell if it was the vet or the rescue) kittens before they were fully weaned.
Interesting how different all the rescue groups are. I give strogid the first day I get kittens, before I even test, even if I get them with a mama. Sending a sample in for each kitten is expensive, and 90% of them have rounds, so we just treat. Worms can be dibilitating and if we don't treat we can end up with dead kittens, quickly. If I see tapes, the second worming will be drontal instead of strongid. If I see loose stools, especially with blood, I bring a sample to another AHT that is set up to read samples, and have her check for coccidia, and if it's positive, I put the kitten on Albon for 21 days (yes, I know the dossage is 14 days, but it's seldom taken care of in 14 days).
We spend a fortune on vet bills, as well as meds and vaccines, but sometimes it's still not enough.
Sometimes it doesn't matter what we do and we lose kittens. If they had been left in the wild the same thing may have happened. We do the best we can, with the funds and volunteers we have. Ferals are the toughest, and hopefully you are keeping them away from your cats..preferably in their own room. Ring worm is easily spread from rescue kitten to home cat. FIP and FIV is another concern, along with feleuk. Once one kitten in a group is dx'd with distemper, the rest can follow, so please, if you are new at rescuing, please be sure to not mix these with your own kittens. I am concerned since it sounds like blood work was done and the white blood cells are up.
We've just hit 360 rescue kittens in our home (at different times of course..just adopted out my last 4..all to the same house!), and so far have only lost one, but that was luck and a lot of work. Working for so many years with a vet has really helped me a lot in assessing these kittens. We've had some very close calls. Unless the rescue group has unlimited funds, sometimes certain tests just have to go by the wayside.
Someone mentioned that they thought these kittens were just a few weeks old. I didn't get that from your post. Can you give us an aproximate age? Are their ears straight up yet? Are they on kitten replacement milk (which can also give loose stools) or they eating on their own? Can you give fluids (which you don't want to do unless they are dehydrated). I would never give fluids through an IV. If they are dehydrated, you just want to give kittens fluids under the skin.
I wish you good luck with these. My internet will be iffy starting tomorrow for several days, but if you have specific questions, or want advice on force feeding them, please pm and I'll try to answer you.
Be sure to let the rescue group know you think the vet should see them again...they may not agree, but at least you will have done your part.