I know it's not "proper" English - but I do think this is a case where "ya'll" or "you all" at least would clarify this is plural.
Yes, you can write "you all", they accepte it usually (for clarification).
Duolingo tends to translate names. Am I the only one who thinks, that non translated names should at least be accepted (e.g. Germania, Italia,... instead of Germany, Italy,... in the English translation) )?