Let us consider a language where the plural personal pronouns are formed using two strategies: plural morphemes and root suppletion.
Thus, something like
I, wes - me, us(e)s
thou, yes - thee, yous
he, she, it, theys - him, her, it - thems
In fact, Finnish is not all too far off from this: in most cases (with the exception of the nominative), the plural pronouns have the -i- plural marker in the expected position. Finnish is also weird by having the nominative/accusative plural marker -t be the accusative marker for pronouns - but even with that present, the other plural marker is present for the plurals.
Anyways, in many languages, there are situations where morphological number is suppressed - one common position for that is after quantifiers (seeing as the quantifier makes the plural superfluous).
We could thus imagine situations where we get
wes saw thems
some of us saw many of them
Now, we can take one additional step to make this idea moderately interesting. Not all the pronouns need to have suppletive plural roots, maybe he and it have no distinct plural root, so "they(masc)" is hes and "they(neut)" is its.
I saw its
I saw hes
I saw three of it
I saw several of him