This is poor reporting. The custody is not with the person, but with the person who wears the Crown. The British Sovereign has legal custody of all of his or her minor grandchildren, to ensure the line of succession. That is now King Charles.
Neither Charles nor Queen Elizabeth could assert custody of Harry's children when they were born until Elizabeth died. Elizabeth had the royal prerogative over her grandchildren (William and Harry from Charles, Peter and Zara from Anne, Beatrice and Eugenie from Andrew, and Louise and James from Edward), who were all grown by the time Harry's kids were born; but the order did not extend to her great-grandchildren, (she had I think nine, including Archie and Lilibet from Harry).
Charles supposedly has legal custody now that he is crowned. The question is whether he is strong enough to use whatever leverage is necessary to assert physical custody of the children, which cannot happen without a fight, or some rather dramatic subterfuge. Philip would have urged the Sovereign to do what needed to be done. Elizabeth was too indulgent, and Charles seems to be, as well.
As for California law versus the British Crown, it would not be hard for UK to turn this into an international relations negotiation between Ambassadors. It would be ironic justice if any custody suit takes place when Trump is president again! Meghi's worst nightmare! I think Trump's parting words to Harry when he saw him last were, "Good luck. You're going to need it."
I said the same at Post 83...
And Trump's last words to Harry were...
First rate reply there Albion... Thanks for sharing. This really could get interesting,...
Harry is a Royal. Meghan is an American citizen residing in California. If she goes to a California divorce court and demands custody, it could get messy, up to the Supreme Court.