I like the change to military uniform, it would demonstrate the Monarchy adapting to the vast change from 1953 to 2023.
I'm sure that if the two non-working Royals were to attend, there would be the usual squawking. However, unlike the Queen's State Funeral, these two shouldn't be allowed to "get their way", particularly for the one who has his own thread.
In addition, for that particular Royal to show up in military uniform wouldn't go down well now with the military and UK public. It would also further inflame the jihadists such as the Taliban and ISIS.