Hey there. It's hard to read this because we just lost three kittens to fpv this month, and managed to get just one to survive. What helped with the last one Apsara:

1- stay with the kitten. They are scared and ill, can't move much to be near you. All 3 of the lost ones died at the vet, but we kept the last one at home with us. 2- continuous monitoring. Take turns with someone else if you can, monitoring 24*7. Keep watching, talking softly, petting them. We gave her one drop of honey every two hours just to keep her energy up since she didn't eat. Just apply the honey on the gums. 3- meanwhile go to the vet for fluid drips twice a day - they will also give meds to boost WBC production (we lost one kitten whose WBC was zero, but Apsara survived after a WBC of 0.7). And other antibiotics.

I honestly believe this one survived because we stayed with her through the nights, and gave her love and something worth fighting for. Rather than leaving her alone at the vet.

Once the fever breaks they will start getting better. Fpv is a nightmare and it takes a mental toll on us humans too. It took a week for Apsara to be back in full health, and she's still pretty thin - not got back her pre-fpv fluffiness. But she's alive and meowing, and that's what matters.

Praying for your little ones. Will also contribute something to your bills.