In my campaign worlds the known deities of a given material plane are always the first mortals who achieved ascension to immortality. My cosmology has thousands of such prime material planes, where all but the youngest ones are ruled by local deities. These deities rule the material plane they come from, and that is the extent of their authority. Many material planes have several pantheons. Any given pantheon is simply a long-term alliance or fellowship of deities who mostly get along with each other, are perhaps related or knew each other as mortals, or who originated from the same region of their home plane. Very few material planes will have only one pantheon, if one is young enough not to have seen many immortals ascend, or if all the immortals still get along with each other. But where multiple pantheons exist there is usually some kind of rivalry between two or more deities which caused a schism between the deific community at large. As with any human community there can be personality clashes, adversarial relationships, competition for divine mates, mortal lovers, devoted worshippers, etc. Deities as a rule are aware of one another's existence at all times, and newly-ascended gods and demigods cannot remain anonymous for long. Therefore any newly-ascended being is usually caught up fairly quickly in the entanglement of alliances and often compelled to "pick a side" in some long-standing, mostly irrelevant argument or feud that began millenia ago.
My feeling is that whatever you want to name your setting's deities, whatever portfolios you want them to have, it's all mostly irrelevant. All that matters is if your deities are semi-realistic, divine NPCs that your players can understand and possibly choose as objects of worship for their characters in-game. If you want to borrow some established pantheon from Deities & Demigods, or Golarion's own pantheon, or use some other homebrew pantheon, it doesn't really matter. Most players aren't going to care what the god of death is called and all of their history of divine existence; it is enough to know that there is one if they want to play a cleric with the death domain, what its alignment and domains are, its favored weapon, and the other in-game details that actually matter to a PC.