All my cats are vomiting and won’t eat.

I brought in 2 outside neighborhood cats(1 year old siblings). One had a litter of kittens. They’re 13 weeks old now. We had some friends come by and adopt 2 of the kittens. Now the two adults and two remaining kittens are all moping around, hardly eating, and throwing up a lot.

Are they just sad or is something medically wrong? It’s only been 3 days but they’ve hardly eaten anything. Seems weird if it’s a medical issue that it happened the night the other kittens left.

I’ll call my vet tomorrow but should I be worried or is this normal with separation?

(The mom seems to care the least lol)