The noun "Beatles" is a proper noun, the name of a group of British singers/songwritiers. A proper noun is always capitalized.
The possessive form of the plural, proper noun Beatles is Beatles'.
The apostrophe following the ending s indicates possession.
Example: The Beatles' songs are still very popular.
The plural form of the other type of beetle, a word for a type of insect, is beetles.
The plural possessive form is beetles'.
Example: The beetles' colors are green and brown.
The plural form for the noun composer is composers; the plural possessive is composers'.
Pianists is plural The possessive is painists'
The plural form of the noun singer is singers.The plural possessive form is singers'.example: The singers' voices filled the auditorium.
The plural form of the noun soprano is sopranos.The plural possessive form is sopranos'.Example: The director rehearsed the sopranos' roles with them.
The possessive form of the plural noun musicians is musicians'.example: The musicians' rehearsal is scheduled for eight.
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'.
The plural of rose is roses. The plural possessive is roses'.
The singular possessive is biker's; the plural possessive is bikers'.