The noun luggage is an uncountable noun, a form of aggregate noun, a word representing an indefinite number of elements or parts. The noun luggage has no plural form.
The possessive form of the noun luggage is luggage's.
Example: The luggage's style was very old fashioned.
The possessive form of the plural noun couples is couples'.Example: All of the couples' luggage was piled in a mixed heap.
The plural form of the plural noun passengers is passengers'.Example: All of the passengers' luggage has been stowed.
Singular possessive: secretary's Plural: secretaries Plural possessive: secretaries'
The plural possessive form of "traveler's" is "travelers'." This indicates ownership by multiple travelers. For example, you might say, "The travelers' luggage was lost."
The plural is lads. The plural possessive is lads'.
The plural is relatives. The plural possessive is relatives'.
The plural form is suffixes. The plural possessive is suffixes'.
The plural form is stepsisters. The plural possessive is stepsisters'.
The plural form is Mexicans. The plural possessive is Mexicans'.
The plural form is echoes. The plural possessive is echoes'.
The plural form is inches. The plural possessive is inches'.
Studies' is the plural possessive of study.