Make a mathmatecal, chemical, or grammatical study of
Third person plural pronoun is THEY.
If you want to create a possessive pronoun out of that one, that would be THEIRS.
Possessive pronouns, as the name itself says, determine some kind of possession. For example:
Is this books yours? - No, it's theirs.
HAVE LIVED
we HAVE LIVED here for ten years now
The answer is Henry was making excuses for not rejoining the fight