change names? Remember, there is Kara-Tur, an oriental setting on the same continent as Faerun. In one game im in, im playing a half drow samurai, whos father came from Kara-Tur. No need to change the name or anything. Just say that they trained under someone from Kara-Tur.
Also, I've seen Rokugan Stuffed into the Forgotten Realms, easy. Conceivably, a character could have travelled to the "main part" of Faerun by ship, or overland routes.
But, if that's not your thing, anotehr name for Samurai could be "sword saint" or like someone said "cavalier". For Sohei, either Templar or maybe "guardian" or similar.