I found that you can have the same name as another character.
How? Like this.
Krelk and Krëlk
Same name, one difference.
If you really want the same name on a character (please don't over use these)
I have made a list of the letters I can find.
ë è é ê
ä à á â ã å
ï ì í î
ñ
ö ò ó ô õ ø
ù ú û ü
ý ÿ
Again, use this only if you really are stuck and don't want to change your name.
I will try to find more.....