Pet = 1 party member, 8 members total.

[Irondude]

PVP would be ether single person (pets are a 1+ to a party so you cant call them) or party PVP up to 8 people. 2 PC vs 1 person and a pet, the two actual players are better. Why are we talking about PVP? this isnt even in the game currently and its going to be a optional thing for fun.

Everybody can have a pet whether its a NPC companion, chocobo, dragon, er goobie?, <insert your favorite thing>. You can only call 1 at a time and it is a +1 to a party.

Different pets do different things, so depending on what job is needed in the party you can use a pet to fill in.
as an example

Drake/Dragon = Damage Doing pet

Chocobo = Damage + conditional healing pet (chocobo dance when a party member dips below 30% health)

Mog = party buffing + healing

companion = job class they are currently assigned

I don't want 8 people and 8 pets on screen at once that's so cluttered!