You need to take a stool sample from each of the pets to your vet's office to have a float done to rule out parasites in each pet. Just walk them on a leash and collect a sample as they leave it. Then label each bag and see the vet with it.
The problem with wormers is that they work for some worms at all. Your vet will tell you which worms are present and can give you an appropriate medication.
Let me know if you still have questions.
