I nipped over to Mumsnet last night and this is being discussed in great detail there too. One thing I read there is that the Q, as monarch, has legal custody of all the royal grandchildren. So I looked it up and apparently it is true. Therefore, if Archie was still in the UK, the monarch could actually seize custody over the parents. Maybe this is why Archie remains outside the UK until "the meeting" is concluded?
More than three centuries ago, a law was enacted that means the sovereign has full legal custody of their minor grandchildren, royal expert Marlene Koenig explains.
The law, called “The Grand Opinion for the Prerogative Concerning the Royal Family,” was introduced by King George I in 1717.