The plural form is mistresses.
The plural possessive form is mistresses'.
Examples: I put the mistresses' mail on her desk.
The plural possessive of "mistress" is "mistresses'."
The plural is mistresses. The plural possessive is mistresses'.
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 possessive of stepsister is stepsisters'.
The plural form is inches. The plural possessive is inches'.
There is no apostrophe at the end of the word mistress. An apostrophe goes at the end of PLURAL possessives ending in -s, not singular ones. The possessive singular of mistress is mistress's, and the plural possessive is mistresses'.
The plural form of the compound noun 'lady in waiting' is ladies in waiting.The plural possessive form is ladies in waiting's.Example: The ladies in waiting's duties include managing the correspondence of the mistress.
Coaster's is singular possessive. The plural is coasters, the plural possessive is coasters'.
The correct form is "its" for the possessive form in the plural. "Its" is used for both the singular and plural possessive forms, without an apostrophe.
The plural is briefs. The plural possessive is briefs'.
The plural is lads. The plural possessive is lads'.
The plural is trollies. The plural possessive is trollies'.
The plural is relatives. The plural possessive is relatives'.
The plural is stations. The plural possessive is stations'.
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive form is heart's; the plural possessive form is hearts'.
The plural form is homes; the plural possessive is homes'.