Thank you for the kind words. I'm a beginner hobbyist with two Nikon cameras. My point & shoot is a Nikon COOLPIX L830, and for more serious stuff, I use a Nikon D3300.
Great question. Try not to overthink it, any ratio is fine.
Examples from last year:
4:3 by @Shabby Chic-Hens
Original
Cropped
16:9 by @Isadora
Original
Cropped
3:2 by @Kluk-Kluk
Original
Cropped
What cameras are you two using?
Since the calendar template is 3375 pixels wide by 2625 pixels tall, smaller images must be stretched to fit.
Both of your entries will be entered in the spreadsheet as "qualified".