There should only be one type of each deity, if possible
In Greek Mythology there was Hades, Cronos (who later took control of the Elesium fields), and Death (who I forgot the name of).
And those arn't all the "death sphere" gods in greek mythology but it gives you the idea of multiple gods of the same type. Though a more well known combination would be Ares and Athena who are both gods of war.
Hades was a god, not the god of death, but more technically the god of the Underworld. I'll give you this one.
Cronos was a titan, and he was usually either still imprisoned in Tartarus (you can think of this as Hell), ruler of Elysium (Heaven) or King of the Cyclops.
Thanatos was the demon personification of death, think of him as the Grim Reaper.
As for Ares and Athena, while they might be both gods of war, Ares focused on the actual warfare aspects while Athena was more of a god of wisdom and intelligence, which included military strategy and not being dumb enough to do dumb shit during wartime.
My point is, gods don't really conflict themselves. There might be two gods in one pantheon who are both "gods of X" but only in the most general sense, if you go to the specifics you'll see that they're not the same at all.
On the topic of the Egyptians and their many sun gods: I don't really know a lot about Egyptian mythology, but I would assume that the case is the same as the Greeks, or they worshiped different sun gods at different eras (like, Ra back in 1000BC then he went out of style and people worshiped Bast instead, that thing).
I like OP's idea. We really should do more with religion. I'd like to see monotheistic cults too, since that's actually a thing (i.e. Christianity is a thing).