i dont think that should happen... although, to be on a safer side, seek permission from an admin or a mod!
if dp doesnt ban accounts by ip , then how will they be able to figure out people with multiple accounts ??
It's probably best to ask the mods, but from past questions like this I read it's ok as long as you two don't bump each others threads.
I thought that was only a problem if you got banned and signed up for a new account. To stay on the safe side ask an mod.
I know of a few on here who have siblings. Katy is a mod and has stated it was ok as long as you let them know. That should cover the question !