When Diana, William and Harry are playing Uno there are a few scenes that uses a Uno Attack shoehorn. Uno attack was first released in 1998.
Forbes Masson develops the pictures in dark room with a red light. A dark room like that is only usable to develop black and white pictures. The photo of Charles and the boys he develops is a black and white image, but is printed as a color image later. (Black and white prints under red light can be made from C41 color negatives.)
Mario Brenna takes a series of photos with his Leica M camera by pressing the shutter button several times in a row. This is not possible with this camera without a motor winder.
The roll of film Mario Brenna is seen taking out of his camera in his darkroom still has the film leader sticking out of the canister, indicating that it had not been used. If it was a roll he had used to take photos of Diana, there wouldn't be anything sticking out, the film strip would have been completely rewound into the canister.
About 16 minutes in, Princess Diana is playing a game with her sons, which appears to be Uno Attack. This version of Uno was not released until 1998, the year after this episode is set.