The proper noun Phish is the name of a rock band. There is just one.
A plural form can be used to refer to the group's members. The plural form is Phishes.
The plural possessive form is Phishes'.
example: The Phishes' outfits can be described as on the casual side.
Note: The word phish (lower case p) is a verb; to request confidential information over the internet or by telephone under false pretenses. The noun form of the verb is the gerund, phishing, which has no plural form.
Singular possessive: secretary's Plural: secretaries Plural possessive: secretaries'
The plural is relatives. The plural possessive is relatives'.
The plural is lads. The plural possessive is lads'.
The plural form is Mexicans. The plural possessive is Mexicans'.
The plural form is echoes. The plural possessive is echoes'.
The plural form is suffixes. The plural possessive is suffixes'.
The plural form is stepsisters. The plural possessive is stepsisters'.
The plural form is inches. The plural possessive is inches'.
The plural possessive of "Father" is, "Fathers"
Studies' is the plural possessive of study.
The plural possessive of bandit is bandits'.
The plural possessive is pals'.