The whales Gracie and George were stated to have wandered into San Francisco as calves. Outside of feeding events which can include the famous bubble nets, humpback whale pods usually consist of a lone mother and calf (or calves) pairing with a trailing "escort" male. Humpbacks are one of the few mammals that can be nursing and still get pregnant. So anyway, the implication seems to be that if they were both calves and coming in the same time as a pod, they must have been orphaned from their mother and part of the same family group. Therefore, when its later revealed that Gracie is pregnant this one question comes to mind:

"Was the pregnancy a product of incest?"

No wonder they were originally going to be called Adam and Evie.