Kitty maybe ingested ibuprofen?

You did the right thing in getting treatment fast. It can be fatal, or cause kidney damage that will also cause them to die. Sounds like the kittens will be fine. The liquid under the skin was just lactated ringers, or water with additives. Because they vomited, he gave them fluids. and if one did eat some, it would help flush through the system. the liquid absorbs into the system to rehydrate.