The proper noun Portuguese is an uncountable (mass) noun, as a word for a person of Portugal or the people of Portugal; and a word for the language of Portugal.
The possessive form of the noun Portuguese is Portuguese's.
The plural of Portuguese is Portuguese.
Coaster's is singular possessive. The plural is coasters, the plural possessive is coasters'.
No. Plural possessive is "their" Possessive pronouns do not use an apostrophe.
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 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'.