The plural form of the noun boat is boats.
The plural possessive form is boats'.
Example: The boats' owners came to assess the damage after the storm.
Theirs is the plural possessive pronoun for 'he'. For example:Mack and Mike bought a new boat, that one must be theirs.Their is the plural adjective for 'he'. For example:Mack and Mike bought a new boat, that must be their boat.
The correct plural possessive form is "your parents' car".example: I see a new boat attached to your parents' car.
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 stations. The plural possessive is stations'.
The plural is relatives. The plural possessive is relatives'.
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'.