Hi Leigh,
Thanks for caring for your litter of kits.
I can gladly give you advice and/or information but I’m very concerned about the explosive diarrhea and vomiting. By now, they haven’t anything in their stomach. Force-feeding won’t do much good if they aren’t keeping it down. They are very little and can’t afford to lose any more weight. I know you have a vet. Appointment tomorrow but I would try to get them in tonight. I know it’s more expensive for an emergency vet purrhaps you can call someone and ask his or her opinion.
Do you know if there’s something in their space they could have gotten into? It could be a parasite like giardia however, since they all have basically the same symptoms, it would make sense it’s something they all access.
It could FIP or Fading Kitten Syndrome. Neither of these have a hopeful end. Here’s information and only a vet. can diagnose these diseases.
https://pets.webmd.com/cats/cat-fip-feline-infectious-peritonitis#1
https://www.petmd.com/cat/conditions/fading-kitten-syndrome-symptoms-and-treatment-options
As far as food, we usually recommend Goats’ milk because it’s gentler on the tummies. If you have someone else around, go get some Goats milk. Some vets. don’t know about Goats’ milk but here in TDKland, we recommend Goats’ milk for kittens. Goats’ milk is full of nutrients, probiotics and gentler on their tummies. This can also regulate the poop. You can find it in the dairy section or the concentrate in the baking aisle. Mix the concentrate 1:1 with water or pedylite. If, at any time, they seem lethargic put a dab of Karo syrup or honey in their mouth.
My first advice is the vet. route as soon as possible.
Good luck
PG