The plural is runners-up. The plural possessive is runners-up's.
The correct plural term is runners up.
The singular possessive is runner-up's.
The singular possessive form is heart's; the plural possessive form is hearts'.
The plural form is homes; the plural possessive is homes'.
The plural of rose is roses. The plural possessive is roses'.
The plural possessive is regions'.
The plural possessive is governesses'.
The plural form is Mexicans. The plural possessive is Mexicans'.
The plural form is echoes. The plural possessive is echoes'.
Coaster's is singular possessive. The plural is coasters, the plural possessive is coasters'.
The plural of senior is seniors. The plural possessive of seniors is seniors'
The singular possessive of "ant" is "ant's" and the plural possessive is "ants'".
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'.
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.
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.