Nope. If you try to log on from two computers, the second login will kick the first login offline. So you cannot have 2 characters from the same account online at the same time.
There also isn't anything like a master account. At least not yet. If you don't want to have your CC info on two separate accounts, the only option you have (at the moment) is to pay for the second account with timecards.
I do think they should allow two instances of the game to run at the same time, but not allow them both to be logged into the same server at the same time, so if, for example 2 brothers want to play, they can share an account, but not play cooperatively on the same server. Which for some would defeat the purpose, but if it's just to play the game rather than co-op up, it should be a workable solution. It would also from the producers/devs side preserve a revenue stream of two brothers/friends etc.. who just have to play the game together, well then you need two subs to do that. Only thing they might be otherwise concerned with is bandwidth, that second sub might be needed to keep the bandwidth affordable, but with F2P coming soon that shouldn't be an issue, and would make a nice bonus for people to make the leap to a subscription.. .mom can buy one sub and keep two kids happy but maybe can't afford two subs... etc.