Wheelock ch. 11 says nostrum and vestrum are partitive genitives and nostri and vestri are objective genitives; I understand that but since nostrum and vestrum have neuter endings does this mean that nostri and vestri are neuter as well?
There is no such thing as neuter endings. This is just syncretism of cases. These pronouns are neither masculine nor feminine nor neuter.
These endings are common to all three genders, so you can’t say that the -um of the partitive genitive is a neuter ending. That said, these, being pronouns, will take on the gender of whatever noun they stand in place of, even if their endings don’t change.
The -um ending is in fact the same genitive plural ending you find in the 3rd and 4th declensions. Gildersleeve’s grammar says that in early Latin texts we find the forms nostrārum, nostrōrum, vostrārum, and vostrōrum for the partitive genitive; presumably the -ārum ending was used when the pronoun was feminine, and the -ōrum when masculine or neuter.
The -ī I’m not so sure about. It does look like the genitive singular of the 2nd and 5th declensions, though that seems incongruous given that these are plural forms of pronouns.
Not to make things more confusing but I will attempt to clarify a common mistake about gender in language.
The endings of a noun (or pronoun) do not determine its gender. However, in the case of normal nouns (and not pronouns) the gender can determine the set of endings used. For example: animus, -i (soul, spirit) is a masculine noun of the 2nd Declension. aurum, -i (gold) is a neuter noun of the 2nd Declension. However, the -s and -m (respectively) endings are not what makes them masculine and neuter – they do change what set of endings you use for each declension though.
Noun gender, to the modern linguist, is quite arbitrary. I would imagine at some point it made sense to the Romans (or I should say I HOPE it made sense to them). The only way for us lowly Latinists to learn a word’s gender is by memorizing the m, f, or n listed (usually in parenthesis like these) in a dictionary.
That being said, pronoun gender is an odd science because each grouping of pronouns has its own set of rules on gender. [Groupings: Personal Pronouns, Possessive Pronouns, Reflexive Pronouns, Demonstrative Pronouns, Relative Pronouns, and Interrogative Pronouns.]
Personal Pronouns: ego, nos, tu, and vos (along with all declined forms of these) have no gender. On the other hand, is, ea, id are m, f, n, respectively and each has its own set of declined forms.
Possessive Pronouns: these all take the gender of that which they are referencing and are declined like adjectives of the 1st and 2nd declensions.
Please let me know if I have raised more questions than answers! Good luck!
Salve!