many people = たくさんの人たち many people = 多くの人たち many people = 群衆 多い人 → 多くの人たち　ならＯＫ 人たち = 人々 暇な時間が多い人 好きなアイドルが多い人 お金が多い人

I think 人が多い (many people) and 人が少ない (few people) is ok.

「多い」「少ない」は「大きい」「小さい」と違い、名詞の状態を表しません。 「多い」「少ない」It is different and doesn't show the state of the noun. That's a special adjective. 「多い」「少ない」の前に「何が多い（少ない）のか」という言葉が必要になります。 It needs the word to which I say "A lot of （few）what is there?" 「多い人」It is a mistake. 「人が多い」It is OK. 「兄弟が多い人」It is OK , too.

Hello Ellen There are several ways to say "many people" in Japanese. The most common phrase used in daily conversation is たくさん（沢山）の人. Or you can say "多くの人々（or just 人）” as well. The second one may sounds more formal and is used in writing more often I think, but we still use it in daily conversation too. Talking about 少ない人, it is not completely wrong in the grammar. But this may sounds a bit abrupt in some case. You may want to use the following expressions instead, depends on what you want to emphasize here. If you are comparing it with other amount, you can use より少ない人々（人々 sounds more natural than 人 in this case) This means "less(fewer) people". If you just want to say "a few people"( not comparing with anything), you can say 少数の人.