I have a player who wanted to get two companions, but not use all of his first level feat points to do so. He decided he was going to take advantage of the feat points awarded to a second tier companion in order to give his companion a companion. This didn’t really work story wise so I shot it down on instinct, but how would that work, being that the player couldn’t command the second companion except through the first?
You are totally within your rights to shut down such shenanigans as a GM, but I also wanted to shine a light on the mechanical aspects of this idea and how it probably wouldn’t have turned out like your player would have thought:
Tier 1 - Your companion has a total of 20 attribute points plus 4 per level of your character.
This means if a companion invests feat points into another companion, than the companion’s companion will always be stuck at 20 attribute points, because companion don’t gain XP nor levels. So that would be a bad investment either way.