One final question for now did the host feed provide oneway talk back to rights holders so they’d get a heads up that a camera change is about to occur or a way for the commentators to know where the cameras coming from?
That's not something that would usually be made available on a state occasion in the UK to other broadcasters.
Commentators just 'say what they see', and joining or leaving you just wait for a shot change and then leave/join soon after.
The BBC domestic presentation truck is likely to have had director-director switched 4-wires to both the chapel and the route trucks (plus bleeds of open PTB possibly if wanted)