Of course, this would merely be a theoretical concern.
But what's also bothering me is that (i) J Jenks, a criminal, probably suspects that the Cullens are not human (ie, he might try to blackmail them) and (ii) following September 11, it is much harder to move around (ie, no more flying for the Cullens because they can hardly risk that fingerprints are taken at the airport...probably they do not even have human fingerprints).
In addition, I feel that advances in technology make it more and more difficult for the Cullens to finance their expensive lifestyle (stock exchange transactions are nowadays tightly supervised; insider trading (that's basicially what Alice does) is tracked and monitored).
Probably, the Cullens should move by car and ship to Africa or South America before the get "locked in" in Forks. They have stayed there for a rather long time anyway.
What do you think?
I don't think these are that big of concerns actually.
1. Jenks is terrified of Jasper. Jenks is himself a crooked attorney on whom the Cullens have lots of dirt. It would be bad for business if word got around that Jenks was blackmailing his clients. It doesn't appear that Jenks has any contact information on the Cullens (he can't call Jasper when he is concerned that Bella is trying to double cross the family, they arrange the meeting ahead of time, he doesn't seem to be aware of where Bella is from). Jasper is very protective of Alice, I think Midnight Sun has a comment to the effect that there is nothing that Jasper wouldn't do to keep Alice safe. All of these things together make me think that Jenks probably wouldn't seriously consider blackmailing the Cullens and that if he did, that Jasper would have many qualms about permanently silencing him if he made the attempt. Personally I think that Jenks's suspicions concerning the Cullens' humanity would make him less likely to threaten them also, on the basis of Jenks not wanting people to think he was going crazy himself.
2. Fingerprinting really doesn't happen that often in airports and the Cullens' wouldn't have criminal records to check the prints against anyway, the bigger concern would be places where they scan people's temperatures before letting them enter the country, though I am certain there are ways around that. The Cullens have Alice to look into the future and let them know if there will be any problems with air travel any particular day and Jasper to make people feel all warm and fuzzy about letting the Cullens go through security with minimal hassle, if they decide to go through security -- my guess is that our vampire friends frequently use their abilities to avoid security lines all together. This is all not to mention their ability to dazzle their way out of situations. There might be a few airports that they avoid, and I would think that long ocean voyages would be uncomfortable because of the lack of blood, but I don't think that we have yet reached a situation where the Cullens are lacking in ways to travel anywhere they like. Especially since they have the means to avoid security entirely through purchasing and flying their own planes.
3. The Cullens' financial situation, I don't think they are in danger here. Again for several reasons:
a. Insider trading laws are aimed at the board members and certain employees of publicly traded corporations (and their families). Since none of the Cullens fit under that umbrella, what Alice does probably doesn't violate the letter of the law (I will remain quiet as to the spirit). Since the Cullens don't tend to make human friends and Carlisle is the only one who is employed it is unlikely that any human could prove that they are behaving improperly with regards to the stock market, particularly if they are using the various legal safeguards that are available to legitimate investors. They also probably have multiple accounts, not just one Cullen family trust. In the shopping with Alice outtake we see that Alice has a credit card with a fake name on it, and my guess would be that fake name has a full credit history and is independently wealthy. Throw in some more fake family trust accounts (the largest are probably off shored to avoid taxes, a la the Kennedys), some shell corporations and perfect vampire recall, and I would say that the stock market probably isn't a worry. There are many, many people and entities with large accounts and many methods Alice could use to blend into the landscape.
b. In Breaking Dawn, Bella says that the Cullens have bloated accounts stashed all over the world. The fact that Alice has a black American Express card under one of her alter egos backs this up. My guess is that they probably have several accounts each in various tax havens under various identities.
c. The Cullens probably aren't paying taxes on all their income. Sorry, I just don't think they are doing it. I personally think that many of their accounts are probably under fictitious identities and I do not think that all of their identities are American citizens. We know they have lived in Canada, and my guess is that their identities there showed them as being Canadian citizens. I also think it is very likely that they have accounts in offshore locations that they just don't report. Or in tax havens. They are criminals after all. As long as they appear to have enough money to support their lifestyle in the accounts that use their actual names, they could probably get away with it so long as they didn't leave evidence of the other identities lying around. And remember, if Alice is buying most of their couture clothing on her alter ego card, there isn't a good way to track exactly how much the Cullens are actually spending.