IANAV (I am not a vet
) but my vet said that coccidia wasn't super contagious. Also the incubation time is around 2 weeks. IT's possible that all your pups were exposed to coccidia but at different times. I would call your vet and ask to drop off a fecal sample. If it's positive for coccidia, the vet will probably prescribe the same meds (normally Albon) as he did for your peke.
How is the Peke doing?