Here in the Puget Sound area, we have endangered orcas (southern resident pods J, K and L), it has been observed that orcas avoid mating with siblings or offspring. With cousins is possible, but they usually mate outside the extended family pod.
Orcas and humpbacks aren't the same of course, but whales are intelligent beings and the expectation that they will simply reproduce with their own children, and between brothers and sisters, is unreasonable.
Left to their own devices, the offspring of George and Gracie would live out their lives and die without producing children.
I would hope that forcing the small family to have offspring with each other (artificial insemination or normal sex) would be against future law.
If they had frozen genetic material/the means to clone why wouldn't the people of Earth future have already repopulated the oceans?
Sadly, within approximately a century of George of Gracie coming to the future, the oceans will be empty of whales again.