Get a calibrator for your display then everybody else will be based on that accurate source.

https://preview.redd.it/t90hid2w711c1.jpeg?width=1000&format=pjpg&auto=webp&s=50aa278b461efc54b6641705ac781524d101dcc4

Put Kevin up front so he looks as tall as his wife.

It’s not about specific lengths, it’s about location.

Get down to their level (good suggestion for animals too) physically lie on the floor if you have to.

Not too close, short lengths make things distorted, 35mm plus is better. Also a longer shot will help provide bokeh in a background with an open (2.8-4f) aperture. Consider what is in the landscape and if the scene is messy.

Patience, your subject will be a crap uncontrollable model 90% of the time. Take lots of pics if your not using flash, burst those shots and disregard all but the occasional good one.