how did Rembrant compose group pictures?

Answer 1

Should read the question properly really. His group compositions tended to be unusual. Whereas typical group portraits of the time would be flat and uninteresting, with all the participants having equal "billing" as it were, Rembrandt tried to inject a sense of drama and movement into his paintings. As a consequence, some people would be less clearly defined as others, which (in the case of The Nightwatch) led to arguments over payment and social importance.

The most famous of his group portraits would be "The Nightwatch" in the Rijksmuseum in Amsterdam.

Its an unusually composed group portrait of a militia group. Not painted at night at all, it was only the dirt that had accumulated on the painting over time that led to it looking dark and earning the nickname "Nightwatch".

See link below.

Answer 2

He was Crossed Eyed, and when he did a single person he closed one eye.