If you see in a book where is says "a people is...", it's because some authors use the phrase "a people" to refer to an ethnic, national, or cultural group, which would be singular. Otherwise, ALWAYS say "people are..."

People are because are is plural.

people are.

In Spanish you would say: "la gente es" because you treat "la gente" as a single unit where as in English it would be the "people are" as this is plural and more than one. It is not treated in the same way as in spanish.

People "are". We use "are" for plural nouns.