Posing
Position the older person first, then let the younger arrange around them. The reverse produces stiffness in both.
In short: Position the older person first, then let the younger arrange around them. The reverse produces stiffness in both.
Shoulder to shoulder, heads tilted slightly towards each other.
Both faces in the same plane of focus.
Quiet, no expression required.
Movement solves everything here too.
The detail frame.
Shows the resemblance more clearly than a front-on pair.
Start with seated together, leaning in — the first two minutes are warm-up and the first pose should be the one that asks least of anyone. Move to one behind, arms around and forehead to forehead once the shoulders have dropped, and keep facing each other in profile for the end, when self-consciousness has gone. Shoot each one in bursts through the movement rather than holding it: the usable frames sit between the instructions, not on them.
Two metres back with the lens zoomed rather than close and wide — distance is what keeps facial proportions natural. Camera at or slightly above eye level for portraits, at chest height for full length. Below eye level enlarges whatever is nearest the lens, which is rarely what you want in frame.
Standing side by side facing the camera, which is the pose everyone defaults to and the one that reads as an obligation.
Treating it as a formal sitting. Shooting only the pair and forgetting individual portraits. And leaving it because there is no occasion — the absence of an occasion is why these photographs do not exist.