Orcs, elfs, and humans of Shivering Isles created by Sheogorath or they emigrated to his realm from Nirn?
Orcs, elfs, and humans of Shivering Isles created by Sheogorath or they emigrated to his realm from Nirn?
Traveled over from Nirn at some point the Shivering Isles isn't one of the realms thats fully closed off to mortals, so would be reasonably easy to get to (in relation to the others anyway). Creating mortal life isn't really something a Daedra would do.
Most of them were probably Sheogorath's fans in life, then they died and their souls went to Shivering Isles.
One of my all-time favorite books within the Elder scrolls world is The Doors of Oblivion in it, is described the many different ways people have found to enter realms of oblivion. As AzuraKnight mentioned it's not totally closed off, it could be that once you go insane that somehow "unlocks" the door for you to stumble into the Shivering Isles. In Elder Scrolls: Oblivion, we do encounter a group of adventurers who are realitively sane, and are given the option to kill them or make them insane, so it can't be THAT hard to find your way to the shivering Isles.
I think all mortals within the Shivering Isles were residents of Nirn, including the Duke and Duchess of Mania and Dementia, both were wood elves. They must have been granted access through the gates of madness. Hence, they were not killed by the Gatekeeper.
Only creations of Sheogorath were possibly the Golden Saints, Dark Seducers, and the abominations found in and around the Isles, Gnarls, Hungers, Grummites etc. To name a few...