Avatars have personal narratives. They can be incarnate, as well.
An immortal hero, warrior, sorceror, and king variously known as Pelinal Whitestrake, Harrald Hairy Breeks, Ysmir, Hans the Fox, etc., wanders Tamriel, gathering armies, conquering lands, ruling, then abandoning his kingdoms to wander again. Just like the Divine Crusader, Ulfric, Tullius, and Dragonborn. They're one person. Keep in mind, the being playing these roles lives outside history. He can be any number of people at once. It's all at once, anyway. Time is coeval.
Pelenial is an unborn robot avatar. Ulfric and Tullius were born of woman. It's a semantic issue. When a god becomes a man, that man is called an Avatar. When a man becomes a god (as Ulfric/Tullius may end up doing) that's called mantling. Yes, this is totally just hair-splitting, but hairs need to be split to keep conversation clear.
And yeah, regarding the part I emphasized, of course every one thing is just the everything is nothing is I, but there's a reason we keep using distinct proper nouns in this forum even though Vivec is everyone and has been for a while. There are layers to the lore, and while on one layer you have this hyper-meta-mystical unitive stuff, on the next layer down (the layer of gods and myths) distinct roles and archetypes emerge, and distinct labels are required. Yet one layer further down (the layer this thread is about - the intersection of gods and men) distinct labels and even personal identities are required.