There's a lot of ground to cover here, and while I'm not an expert, I'll try to answer what I can!
In regards to the Twelve and Primals:
The gods are real entities- they were partially summoned during the Calamity by the collective faith and effort of the people of Eorzea as a means to protect the world against Bahamut. Typically, they do not have physical form or tangible influence in the world- much like the Primals. The Primals are entities that operate on the same axis of existence, but are not in the main pantheon and are instead worshiped by the beast tribes. Get enough crystals and dedicated believers in one place calling for a Primal to take physical form, and it will emerge from the aether in a tangible body.Â
Of course, the beast tribes make a concentrated effort to repeatedly summon the Primals, while the people of Eorzea typically don't put in a lot of energy into giving their gods physical form. Primals and gods alike can lose their physical body and therefore their means to impact the world around them, but cannot be permanently killed. They're forces of nature that simply exist. And Primals are a little more complex than just "they're the bad guys". They're entities that are clearly motivated to continue to exist in the physical world, and tempering exists as a means to an end to have a dedicated number of followers to maintain the faith in them necessary to let them stay in the physical world. But each of them has individual traits- Ifrit is more avid to temper mortals, and wishes to cleanse the world in holy fire, while Titan is more concerned with serving as a protector to the Kobolds, particularly at a time when they've been wronged by the people of Limsa Lominsa. Garuda wishes to eliminate her competitors for worship, and is vicious and capricious, to the point that not even all Ixal are 100% behind her existing in physical form. We haven't seen them face-to-face yet, but it seems like Ramuh is a benevolent protector in the vein of Titan, while Leviathan is more Ifrit-like and demanding. All of them are to some degree motivated by a desire for worship and a connection to those with faith in them, and all of them would prefer to exist in tangible, physical form.
In regards to the Twelve and Primals:
The gods are real entities- they were partially summoned during the Calamity by the collective faith and effort of the people of Eorzea as a means to protect the world against Bahamut. Typically, they do not have physical form or tangible influence in the world- much like the Primals. The Primals are entities that operate on the same axis of existence, but are not in the main pantheon and are instead worshiped by the beast tribes. Get enough crystals and dedicated believers in one place calling for a Primal to take physical form, and it will emerge from the aether in a tangible body.Â
Of course, the beast tribes make a concentrated effort to repeatedly summon the Primals, while the people of Eorzea typically don't put in a lot of energy into giving their gods physical form. Primals and gods alike can lose their physical body and therefore their means to impact the world around them, but cannot be permanently killed. They're forces of nature that simply exist. And Primals are a little more complex than just "they're the bad guys". They're entities that are clearly motivated to continue to exist in the physical world, and tempering exists as a means to an end to have a dedicated number of followers to maintain the faith in them necessary to let them stay in the physical world. But each of them has individual traits- Ifrit is more avid to temper mortals, and wishes to cleanse the world in holy fire, while Titan is more concerned with serving as a protector to the Kobolds, particularly at a time when they've been wronged by the people of Limsa Lominsa. Garuda wishes to eliminate her competitors for worship, and is vicious and capricious, to the point that not even all Ixal are 100% behind her existing in physical form. We haven't seen them face-to-face yet, but it seems like Ramuh is a benevolent protector in the vein of Titan, while Leviathan is more Ifrit-like and demanding. All of them are to some degree motivated by a desire for worship and a connection to those with faith in them, and all of them would prefer to exist in tangible, physical form.
