Yes it's a photo-montage. Top left and bottom right cats were already ex when top right and bottom left photos were taken.
I chose 4 photos with grass background to give a consistent look but had to juggle with the colour balances to compensate for the different lighting conditions.
You're both right, CG and Ali.
Oliver Walter "Ollie Wally", bottom right was an absolute sweetie. (the only boy)
Maisy, top right was smaller by at least 1kg and 3 years younger than Flora, top left; but made her life an absolute misery with constant bullying.
For completeness, bottom left is Chocky (Flora's sister from the same litter), named so because she was a lovely chocolate brown kitten. No sooner had she acquired the name, she turned jet black.