Multilogging rule and how not to get banned for it:
Muling: Stay in town while you are muling. Do not leave your mule in town while you kill monsters with your character.
Two or more people on the same IP: Make sure that either both of you are playing (killing monsters) or both are AFK. If only 1 of you needs to be AFK, then he should quit the game and rejoin later. You may still get the warning, but you won't get banned if you follow this.
Also, do not eat any Signet when multilogging since bot will consider that as leveling a char. Additionally, do not self-rush and do not attempt to multiwindow with more than 2 characters at once. Any offenses here can lead to a temporary ban for first offense. First account ban is typically 8-24h, second 48-72h, third is permanent.