Все=plural, весь - masculine, вся - feminine, всё - neuter. They can be used separately as pronouns also, especially все: все вернулись живыми=everyone has come back alive. Also, всё is used like это (also a neuter pronoun) and kind of agrees with it meaning "всё это": "всё напрасно"=всё это напрасно="everything is in vain".
This does seem to be what we're being taught, as if все and всё are strictly different words, with different pronunciations. But I also recall (I wish I could remember the context) that there is a tendency (rule??) that when "е" is stressed, it becomes "ё". Is this true, and if it's not limited to specific contexts, in some sense could they really be perhaps becoming the same phoneme? This would explain why Russians seem so lax about distinguishing them in written text. If that's true, perhaps what we're calling все and всё are actually homonyms in practice, even if they are spelled differently (like pale and pail in English, or even spelled the same, as bat in baseball vs. bat the animal), and pronounced either way, based solely on stress. Russian linguists??
I'm still trying to get a handle on the whole "все" vs всё" thing. Would it be correct to say that "все" with NO DOTS is used when referring to all PEOPLE whereas "всё" WITH THE DOUBLE DOTS is used for all THINGS? Also, are they pronounced differently? The audio on Duolingo seems to pronounce them the same, but I thought "е" and "ё" made very different sounds.
все = everyone, everybody (with no noun) Все здесь. Everyone's here.
все (with a noun) = all .., all the... Все студенты здесь. All the students are here. все вещи = all the things
всё = everything (with no noun) Всё здесь. Everything is here.
But всё is just the neuter form of весь/вся/всё (there are other case forms too), which mean 'whole/entire' with a noun. весь день = all day вся книга = the entire book всё окно = the whole window
Etymologically it is. Russian is one of the few lucky languages which etymology is quite studied and described. For instance, in Vasmer's etymological dictionary (most fundamental), in Russian it is Этимологический словарь Фасмера, it's easily found online (for instance, first link in google).
I can see why it wouldn't be accepted in the reverse tree, and if you are a native speaker you'll understand that this sentence (referring to a specific group of people) is much less likely to occur. But to answer your question, and mine below, I asked my hubby who is a native speaker. For yours he said, "Все люди разные." Bravo. So you might want to report it.
For mine (I had translated 'all different people'), he asked, "Well, can you say it in a sentence?" I could not. I would have to add a word at least, for example, I could say, "the group was composed of all different types of people." Awkward. And even asking him to just translate the fragment, he said you'd just say, "люди разные."
This reply seems to ignore the fact that the use of "all men" to "mean all members of mankind" is still correct English (although less fashionable nowadays). "All the men" would be incorrect, because that would assume that a group of males were referred to, but I do not see why the answer that Wentris gave should not be accepted.