Sentence Correction

hi

i am confused with this

Friendship was something James truly valued, so he disliked it when they talked about him behind his back

This sentence is wrong because "they" do not has referee friends

Then why these below are correct

James and I went on a picnic together
Who are you going to marry

Here "I" do not have a referee
"Who" and "you" do not have a referee

please help

'they could refer to anyone. "I" and "you" are unique references to a specific person.

Can you please elaborate