They only put the "all" to make us understand it's a plural you, but it's optional.
Please, report with the report button when you see something that could be accepted and that is not (because commenting here is useless, unless there is a grammatical trick in the sentence you want to explain ou be explained.)
"You would like our books." was the suggested correction for me, so either you did a typo in your answer, or they have since added it.
In any case, just report and wait.
Latin adjectives (and nouns too) conjugate based on the case (nominative/accusative etc.), the number (singular/plural), and the gender (masculine/feminine/neuter) of the noun. Here, the noun "libros" is accusative (because it's a direct object in this sentence), plural (multiple books), and masculine (because "liber" simply is a masculine noun). So we need the masculine accusative plural ending on "nostr-" (and on "libr-"), which is "-os."
"Nostrum" and "noster" (among other forms) represent other case/number/gender combinations, respectively masculine accusative singular ("Librum nostrum velitis" = "You would like our book") and masculine nominative singular ("Liber noster in mensa est" = "Our book is on the table").
That is a lot to consider. So I'm wondering if the noun 'our' is referring to is in whatever declension, our just follows that declension? 99.9% of the time maybe?
Looking for a way to simplify the process in my mind if you understand what im getting at. Thanks for the response(s), I'll be sure to follow up on the links.
The adjective will frequently have the same ending as the noun, but often the adjective will follow a different declension pattern than the noun does, and so it will have a different ending.
"Pater" for instance follows a different pattern from "liber", but "noster" will still follow the same pattern it does for "liber" ("pater" is third declension instead of second, but "noster" only follows first and second declension patterns). So for instance in the plural accusative, we would have "patres nostros amamus" ("We love our fathers"), where "nostros" takes a (second declension) masculine accusative plural ending to fit with (third declension) "patres," but since they're different declension patterns, they get different endings.