Hi, Welcome to HCM, You are right that dogs are carriers of pertussis bacteria. Pertussis is whooping cough caused by a bacteria called Bordetella pertussis. I also understand the paranoia of the new parents as they wish for a safe environment for their newborn. I also can connect with your feelings as I have a pet at home who is like a family member now. I suggest you have a talk with them and they could talk to the vet who is seeing your cats and he can assure them safety of their baby. The babies are also universally immunized for pertussis infections, so your grandchild is safe if he is being vaccinated as schedule. However we cannot rule out other diseases caused by pets like most commonly allergies, parasitic infections and they can injure the baby as they are also curious about the new member in their house. I hope I have answered your questions satisfactorily. Thanks.