As much as I'd like to imagine that was the intended meaning, I'm pretty sure 'them' just means any group of more than one object...
In a similar vein, I got marked off for guessing 'He has eaten her'...but why couldn't it mean that?
"She" would translate to "ze" only as the subject of the sentence, as object it is always "haar". Here in this sentence "ze" is used as an object, so it has to be "them". Your suggestion "he has eaten her" would be "hij heeft haar gegeten". [Flemish speakers may often use "ze" for "her" in object form, but this is not correct in The Netherlands.]
It's because hun is used as an Indirect Object, while hen is used as a Direct Object or after a preposition. Both hun and hen are used when referring to people.
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Btw, hun can also be a possessive determiner (but not in this case, of course).
"Hun" is strictly possessive, the mistake of using "hun" instead of "ze" is made by Dutch people all the time, but it's absolutely wrong.
It's accepted, though keep in mind that hun and hen are only used when referring to people.
No, as the object of the sentence ze = third person plural.
Third person singular female can only be haar.