Generally, you can only get 'one' familiar, as pretty much all sources refer back to the wizard class to determine how it works, and the entry for familiars specify adding together all levels to figure out the effective wizard level.
Now, there is no explicit line of text that says you can't have more than one, but the language is written in such a way as to never acknowledge having more than one. Even familiar-adjacent abilities (like bonded items, or blackblades) specify that you can't have that ability and a familiar at the same time. There may be some exceptions where a specific class feature (or a spell) allows for more than one at any given time, but you have to examine those individually as they come up.
“3 feat pet” isn’t really fair. Possessed hand is a +1 to attack and damage with some other minor perks. And autonomy is an improvement to dual wielding with some other minor perks. People will certainly stop on either one of those feats and never progress to detachment.
“3 feat pet” isn’t really fair. Possessed hand is a +1 to attack and damage with some other minor perks. And autonomy is an improvement to dual wielding with some other minor perks. People will certainly stop on either one of those feats and never progress to detachment.
Its totally worth it to progress the hand to the Detachment stage, simply to get access to familiar archetypes.
It can be worth it, but it’s not the default assumption on taking the first two feats. The first two feats are pretty solid on their own. And it is slightly counter to the 2nd feat, as dual wielding is harder when you are down a hand.
What are you looking to gain by having multiple familiars? Familiars are not good combatants so having multiple familiars to fight for you is not going to be that helpful.
Normally when you have multiple classes that grant familiars they stack with each other to determine the abilities of the familiar. The following was from the familiar section of AoN. “Levels of different classes that are entitled to familiars stack for the purpose of determining any familiar abilities that depend on the master's level.” That indicates classes with the familiar class ability do not gain multiple familiars.
Benefit: You can remove your possessed hand, allowing the possessing spirit to animate and control its motion. Removing or reattaching your possessed hand is a fullround action. This deals no damage to you, but you can’t use the hand while it is removed. The hand acts as a wizard’s familiar, using your character level as your effective wizard level, except it doesn’t gain the alertness, share spells, deliver touch spells, spell resistance, or scry on familiar abilities. Use the statistics for a crawling hand (Pathfinder RPG Bestiary 2 59) to represent the detached hand, save that the hand isn’t undead, doesn’t have the mark quarry ability, and shares your alignment. If the hand is destroyed, the spirit regenerates your missing hand in 2d4 days. This process can be accelerated by regenerate or similar magic. You cannot use the Possessed Hand feat or any feat with the Possessed Hand feat as a prerequisite until the hand is fully regenerated. If you have the familiar class feature, you for your possessed hand to become your familiar, granting it all familiar abilities as normal. If selected as a familiar, your possessed hand grants you a +3 bonus on Sleight of Hand checks.
The Hand’s Detachment feat says it acts as a familiar, but it gives the option of choosing for your detached hand to become your familiar. That fact it gives you a choice indicates that if you do not want the detached hand to become your familiar it does not. The detached hand does not gain all the abilities of a familiar (unless you choose for it to be your familiar). The detached hand is not really a familiar it is just using some of the stats of a familiar to define it. So, you could have a detached hand and a familiar, but unless the other ability granting the familiar has clause similar to Hand’s Detachment you cannot have more than a single familiar and a detached hand.
I am also pretty sure you cannot use familiar archetypes with Hand's Detachment. Since the Detached hand lacks the abilities those trade out it does not qualify for the archetypes.
I am also pretty sure you cannot use familiar archetypes with Hand's Detachment. Since the Detached hand lacks the abilities those trade out it does not qualify for the archetypes.
You are correct that it wont qualify for those archetypes, unless you choose it to be your actual familiar.