We need more car for Royals ( Roll royce Ghost, New Phantom, Bentley, Bentley Mulsanne), Jaguar XJ, Aston Martin DBS and DB5 and 6, BMW 750LI, BMW X5 AND X7, porsche 911, Ferrari 488, Lamborghini) and need more house for royals.
Hello Leon 
In terms of the vehicles you are suggesting, I personally think that that would be way too many for the Monarch to choose from. Also, the Prime Minister has used the Jaguar XJ in the past in real life, but the Monarch has never to my knowledge, so it would be unrealistic. It would also be unrealistic for them to be driving supercars.
The suggestion of adding more Royal Residences is linked here: More Royal Buildings