Board Thread:Questions and Answers/@comment-31594898-20170326105723/@comment-93.16.135.125-20170326121235

1/ It's very unlikely because it's a paradox, but it's probably not impossible. The Third War had two aspects of the same Saber summoned together as 2 Servants by the Edelfelt sisters, they were also both Sabers  so that's a bit of a special case.

2/ Different aspects of the same person, different time in their life, slightly different personality from the difference in experience: although they'll both remember their entire life, they were probably in a different mindset in the age they were summoned as. I don't get what you mean by "totally different beings." They're two guys standing next to each other who happen to have the same mind and memories. Kid Alexander and kid Gilgamesh in Grand Order have their memories from being an adult but have a cheerful personality as a kid.

3/ The Caster Gilgamesh in Babylon is the one that's still alive, he sealed his treasury and stopped adventuring to rule his country, but he still uses magic from a distance, so he's a Caster. Then he dies and his spirit lingers in the Underworld, and he has access to his treasury (and Ea) so he becomes classified as an Archer.