Question about 'in a queue' and 'in a line'

[konungursvia]

"Standing in a line" simply means that that is the shape they are making. It could be a police line-up, maybe they're standing aside against a wall so that a large vehicle can squeeze past, perhaps they are part of a living sculpture.

"Standing in line" (AmE) = "queuing" (BrE) = "waiting for their turn"

Standing in a line (AmE) = Standing in a line (BrE)

Exactly. In gym class, we often tell Canadian kids to "stand in a line" but this does not carry the implication that anything will happen in order, i.e. either left to right or right to left.

For that, we say stand "in line" or "line up."