A Cambridge Dictionary post says
We use all of before personal pronouns (us, them), demonstrative pronouns (this, that, these, those) and relative pronouns (whom, which). The personal pronoun is in the object form:
I need to speak to all of you for a few minutes.
I used to have three pens but I’ve lost all of them.
whose object are "you" in this case? How about "them"?
I am aware the concept of object,
a noun or noun phrase that is affected by the action of a verb or that follows a preposition
In the sentence "I like ice cream", "ice cream" is the object of the verb "like".
I also aware that "you", as a pronoun, could play a role of object. In the sentence "Alice likes you", "you" is the object of the verb "like".
I don't understand whose object are "you" and "them" in first two examples. I don't understand the term "object form" either. Could someone please give a hint?