From what I know, the plural noun "people" is люди when no numeral precedes it. Whereas "people" preceded by a numeral take the stem человек-, as in два человека, пять человек (the latter example meaning that "человек" is also an irregular genitive plural).
In the aforementioned examples, the numeral is in the nominative case. If number 2 ever takes the animate accusative case (which does not concern numbers from 5 forth), then we'll get двух человек which is usable either for the genitive or accusative case of this numeral-noun sequence.
But what if I ever want to write a numeral-people sequence in other cases? I namely want to tell "between two people". Will it become Между двумя человеками?
Someone told me it should be rather "Между двух людей", an expression which, if correct, then adds up to the long list of irregularities in the Russian language, since между takes the instrumental case by default, and людей is being used after a numeral.
So, which is the right word for "people" after a numeral taking the dative, instrumental or prepositional cases?