All the PC I already know, we all play together every week and switch of campaigns who is Gm ect. So I am not worried about any of that. This is a one shot, with multiple sessions.
"Will we explore our character's pre-amnesia lifes? If yes, how can I be sure that you as a GM won't make me uncomfortable with my own PC?"
- Yes they will get flash backs from time to time, either in a dream or if they see something that triggers a memory. As far as being uncomfortable with your character I personally can not see that happening, if so they shouldn't be playing this particular game. But like I said I know all these players and we talk/play all week so know that will not happen.
"Who banished the PCs to the island? Why? Is this common? Do all banished people suffer amnesia or was it a fluke, just this time? Why the amnesia?"
-Different people this campaign is set in a world that if a criminal is deemed to evil or not worthy of a quick death/think they can escape from prison they are sent to this banished island where they have to die of hunger/thirst/simply loose their mind. Commonish? I mean how often do you get super evil people walking around. They co-gm and I are still deciding if the island makes you loose your memory, or if was something else so would have to get back to you on that one.