Yes
As far as the public knows? Quite randomly.
From the common street rat that is the Lord of the Shadows to the highest Queen Trinity of the Lady of The Sea, the island doesn’t seem to have much of a preference.
Yes, but for some reason, the island doesn’t always fill them.
Half, maybe less. Though there doesn’t have to be a black parade for a deity to die.
Some deities of the dead do not wish to stay in their realm, surrounded by darkness, shadows, constantly managing the afterlife. Though there are some deities of the dead whom are content with it and they don’t always have evil and chaotic tendencies.
They do so quite regularly, actually. Those below experience these as abnormalities in the physical realm such as the tides going the wrong way or rising and falling on odd times, earth quakes, week long rains,year long winters, etc. Usually, the dispute solve themselves, but when they don’t, one is most likely slain, or is forcefully exiled.
If a deity of the dead is slain, a new one will most likely be selected by the island after a month or so. During which, the dead will reign free throughout the land of the living until the new deity assumes control.
No. When a deity is slain, their powers return to their title in which the the island will most likely find a replacement to give.
I’ll clarify what I said about the occupants of each realm. It is not the number of deities are actually alive. It’s how many titles are in that realm. Some titles are temporary, most are permanent. The powers are bound to the title, not the ascended.
There is the odd case of The Lord of the Shadows. He is slain in the 2nd Black Parade, but the island never ascended a replacement for him, nor was his powers distributed amongst the other lords and ladies, and thus leaving the question, where did his powers go?