I think the message is very clear - the monarch and her three heirs are the future and, other than for personal milestones, I wouldn't expect to see any 'staged' pictures that aren't of these four. These are the future of the monarchy.
If the rumours that Charles wants a smaller royal family - that doesn't include siblings then, at some point that will also mean Harry is out.
Given the Andrew situation I can see them further restricting the 'working royals' to just the heir and spouse in each generation (four working royals in total).