For starters:
http://www.graalonline.com/docs/agreement
Section 4 states that company owners and administrators get to decide what is fair and acceptable use during play.
Presumably since account sharing gets people banned all the time, it isn't fair or acceptable use.
I think old p2p's had a second agreement they signed upon registration that outlined account sharing more explicitly, but I'm not gonna dig that far from my phone. Will edit if found later