Learn English – Meaning of “earn their keep”

A bit of "poetic license" is often necessary in order to make a poem have correct rhyme and meter. In this case, "in their turn" is simply a way of saying "when the right time comes"; as you say, that time may be immediate.

But there may also be delays; if you manage to avoid getting zapped by the vault door, you can take as long a break as you want while packing up the gold before you have to confront the dragons at the next security checkpoint. And if by some miracle you do escape from the vaults entirely, there's still likely to be a team of bank enforcers hunting you down eventually, so "your turn" (to be punished) will still come, and then you will "pay most dearly."

in some English speaking countries, when a woman gets married, her last name (her surname) is changed to match that of her husband.

Professionals have more and more frequently been leaving this custom behind, thus the phrase/idiom keeping her name.

I saw this in a wedding announcement in the New York Times: The bride, 37, is keeping her name. She is an assistant professor of anesthesiology at Columbia University Medical Center and is on the staff of ...