How the heck do I link an account??

Okay so basically this is the issue.

So I have one character right now, Eden, but I want to introduce one of her siblings (either her brother or sister who she hasn't seen in like a year, yadda yadda) but when I went to go make the new account, it wouldn't let me. See I was just going to make the account and link them which I thought would be simple. But what happened was it said that I already was registered and so I couldn't make a new account because you can't do that anymore.

So am I missing something? Is there a way to make an account for one of her siblings that I just don't know about?

Thanks,
-Nadia (Eden)