Cats are just like a new born baby and need to be treated as such.
Make sure that they do not dehydrate by taking them to the water bowl. If they will not drink take some water up with your fingers and gently touch the cat’s nose with the water. If they are thirsty they will get the hint and drink. Maybe not a lot depending on how sick they are but it’s important to make sure there is water for them.
If they still do not want to drink water and will not eat try this recipe
Take one raw egg and beat until all the albumin is broken up. Add a bit of tin fish to give it flavour and a quarter asprin. Beat until changes colour with a fork and offer it to the kitty.
The egg will both rehydrate and put a energy into the cat.
After two or three eggs you will start to see a difference in the cat.
If not get it to the vet immediately.
I am not a vet but this worked wonders with my kitten.