The word polite is an adjective. Adjectives don't have singular or plural, they have degrees, for example:
The noun form for the adjective polite is politeness; the plural form is politenesses.
you ( plural or polite form)
You cook (plural, polite and familiar in Spanish-America; only plural polite in Spain) They cook.
The word "ma'am" is a noun of polite address, a contraction for "madam." The plural is "mesdames." Another polite address form is "ladies."
You learn (informal / polite you, plural in Spanish-America; only polite in Spain)They learn
The word for polite actions (plural of courtesy) is courtesies.
You give (polite you, plural) They give
Ustedes son- You are (polite form in plural)
Familiar: tu, polite: lei, plural: voi
Present indicative of "alquilar" for:You rent (polite / informal, plural in Spanish-America; only polite in Spain)They rent
You fired; you said farewell (polite or familiar you, plural, in Spanish America; only polite in Spain) They fired; they said farewell
Come in (plural you, polite or familiar in Spanish America; only polite in Spain) Present subjuctive (presente de subjuntivo): May they come in May you come in (polite or familiar in Spanish-America; only polite in Spain)
"Ustedes" means "you" in the plural, the polite form