I never played original pathfinder let alone on fantasy grounds.
When i have have people playing a class with a pet in dnd5e i usally make a pc with the stats of the creature they have and its under their control.
In pf2 i found that the the character sheet is locked up so i'm unable to manually change the stats. so i went into the db.xml file and started editing and discovered that the <abilities> are dictated by the <chargentracker>.
So should i just scrap this idea and make a npc entry to use as the animal companion or just keep on going.