Люди is the plural of человек, except when it's after numerals. "People are happy" - Люди счастливы. "Thirty people" - Тридцать человек. (See section 'Usage notes' here ). Note that this sentence (два человека) cannot possibly use люди anyway, because два requires a noun in singular form genitive case.
But the lesson instructions said to use людей with numbers under 5...?
"When you are counting people, use "челове́к" for numbers that end in «пять» (5) or more. Anywhere else use the normal Genitive plural "люде́й" (with много and мало both are possible, but I'd stick to люде́й)."
I think the lesson notes are incomplete. You use:
- «челове́к» for numbers that end in «пять» (5) or more. (and «один» (1))
- «челове́ка» for numbers that end in 2, 3, 4.
- there are special "collective" numerals that can only be used in certain cases. Such as «двое» (2) or «шестеро» (6). With these numerals you can use both «людей» and «челове́к» (but not «челове́ка»).
- if there are no numerals, always use «люде́й».
You definitely cannot say «два люде́й», it doesn't even fit grammatically.
Interesting pronunciation. It sounds more like the word is spelled "человейка" - but a recording at forvo.com backs up the computer, https://forvo.com/search/%D1%87%D0%B5%D0%BB%D0%BE%D0%B2%D0%B5%D0%BA%D0%B0/
Two young people = два молодых человека
молодых is a genitive plural adjective
человека is a genitive singular noun
I believe that два is nominative masculine/neuter plural
Does anyone know anything about this oddity of grammar?
Right... Seems like I still have a lot to read before saying something really wrong there.
Please don't use Russian italics. Reading Cyrillic is hard enough without having to realize that т is actually Russian italic "т", not some form of "m". I suggest using bold for the mark-up language here (**[word]**)
Numerals are accepted when translating to English. Not what translating to Russian, because they want to make sure you're actually learning the names of the numbers.
Does everything have to be so stereotypical? It should be "two people" because a man is only one gender in a race of two genders!
"Two people" is the suggested translation so I'm not sure what your problem is.
Also, I could be mistaken on this one but I do believe I've read from native speakers that "человек" sounds odd if said about a woman and it most likely does mean a man.