The sneezing is not from the fleas. It's probably more a respiratory illness that they are passing around. If the discharge from the eyes or nose is green or yellow, you need to see the vet for antibiotics. Otherwise, you can wait and let this get better on its own.
The fleas can be more of a problem and can cause hair loss, itching, rashes and even anemia. You need to go ahead and swing by the vet's office and pick up some frontline for each of them.
Let me know if you still have questions.
