There is no simple answer to this question. The best way to know your words (singular or plural, and possessive forms) is to increase your vocabulary (the number of words that you know and recognize).
Most plural nouns are formed by adding an "s" to the end of the word (apple, apples; bell, bells).
But many plural nouns do not end with an "s" (child, children; foot, feet).
Some nouns do not change from singular to plural (one deer, two deer; one aircraft, two aircraft).
And some nouns do not have a singular form or a plural form (barracks, oxygen); these are called mass nouns or uncountable nouns.
Possessive nouns are indicated by adding an apostrophe s ('s) to the end of the word, or just an apostrophe to the end of a plural noun that ends with an s (s').
Examples:
The word sisters is the plural form; the plural possessive is sisters'.
The word wife's is singularpossessive.The plural form is wives.The plural possessive is wives'.Examples:My wife's birthday is on Friday.Well, what do you know, our wives' birthdays are the same day.
The plural form for the word Williams is Williamses. The plural possessive form is Williamses'.example: The Williamses' house is the one on the corner.
The word its is the possessive. It is singular and does not require an apostrophe when it's possessive. The plural form is their.
The plural of niece is nieces. The possessive form for nieces is nieces'.
possessive plural word for the bishops: bishops'
The word sisters is the plural form; the plural possessive is sisters'.
The plural possessive is dimes'.
The plural of niece is nieces. The possessive form for nieces is nieces'.
The plural is queens. The plural possessive is queens'.
The plural is inventories. The plural possessive is inventories'.
The plural is stars. The plural possessive is stars'.
The plural possessive form is glasses'.
The word wife's is singularpossessive.The plural form is wives.The plural possessive is wives'.Examples:My wife's birthday is on Friday.Well, what do you know, our wives' birthdays are the same day.
The singular possessive form for stockholder is stockholder's.
The singular possessive noun is chair's; the plural possessive form is chairs'.
The singular possessive is author's. The plural possessive is authors'.