Worms- how long to get rid of?

I rescued two kittens over 2 weeks ago. They went to the vet exactly two weeks ago. I knew they had worms b/c someone vomited and I saw them. (Round worms). The vet gave them a dewormer and gave me a dose to give after two weeks. I gave that last night. Today I found a worm in the poo. It was bigger than the ones that were vomited. Suzie is due back in two weeks and Jelly goes to his new home this weekend, and will be vet checked by my friends vet. I did notice that he still had a bit of a pot belly.
Is this worm just the last of it coming out of the system? Does the wormer cause those remaining to die and be passed? I've never had a cat with worms before. The cats are healthy as far as I can tell, are growing like weeds and playful. They eat quite a bit and their poo is somewhat soft.

Usually 2 doses 10-14 days apart takes care of them, but there's always the chance that twice is not enough. It's also possible what you are seeing is dead worms passing, but I would call and ask if you can bring in a fecal sample for testing to be sure.

Multiple dewormings may be needed. The dewormer only kills mature worms, not larvae. If both cats are getting a checkup in another two weeks, just make sure that a fecal analysis is done. Wait at least two weeks after the last deworming for the analysis. It doesn't have to be done on the same day as the checkup. A stool sample can be brought in any time.