Answer:
Metonymy
Step-by-step explanation:
The first thing I want to look at is the definition of each figurative device.
Metonymy - the substitution of the name of an attribute or adjunct for that of the thing meant, for example, suit for business executive, or the track for horse racing.
Synecdoche - a figure of speech in which a part is made to represent the whole or vice versa, as in Cleveland won by six runs (meaning “Cleveland's baseball team”).
Metaphor - a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.
Apostrophe - a speech or address to a person who is not present or to a personified object, such as Yorick's skull in Hamlet.
After looking at these definitions I have concluded that the correct option is metonymy referincing to "Crown" as being a replacement to the royal family or the king in either case.