As I know they allow to have multiple pen names on one account. They don't allow to have multiple accounts to them. Guess that they check the IP, at least if they ban your account and you want to open another one.
If you use different information to open an account, then it's possible. Suppose, you've 3 family members using a single PC, all can create a/c. But I think, we don't need more than 1 a/c.