A distinction must be made between “accounts” and “game characters”.

An account (S&F account) may contain several game characters, but a game character can only be assigned to one account.

Each user may use only one game character per game world. If a user simultaneously plays with more than one game character in the same game world, this can be penalized with a permanent ban of all involved game characters. You are allowed to create characters on different game worlds though. 

Please also note that sharing an S&F account or characters with (an)other player(s) is also prohibited.