"I do not see them."
Translation:Ik zie hen niet.
Hun and hen can't be for inanimate objects. Ze can be.
Hun=their (possesive) and them (indirect object without preposition)
Hen=them (direct object and indirect object with prepositions)
Ze=she/they (personal pronoun) them (direct object and indirect) (though ze won't always sound better than hun or hen)
Ik geef het boek aan hen
Ik geef hun het boek
Ik geef ze het boek.
Ik geef ze hun boek.
I admit it is difficult to wrap your head around. Mine is spinning now and I don't know what sounds normal anymore..
Whatever you do don't ever use hun as the subject.
Edit here is some extra reading material https://onzetaal.nl/taaladvies/hun-hen
For humans if it's a direct object always hen, if there is a preposition in front of it, hen
In the other cases, so indirect object without a preposition you can use hun.
Ze is accepted for both of them and works with inanimate objects too. (Ze can't replace hun in its function as a possesive though)