I have two roomates that want to move out without giving 30days notice. They are also saying they will not pay for the entire months rent. Can they legally do this?

I better start this off stating I'm NOT a lawyer, but I know several landlords who rent out various properties in VA to various tennants, commercial and residential.

You can always take them to small claims court if nothing else works (once they have vacated the house) or they may retaliate by paying nothing and forcing you to go through and eviction process costing your time and money out of spite. (Sorry but I'm not a trusting sort of fellow).

You do have to be careful what you do while they are still living there however, so get a clear answer from someone with the local realestate law experience before changing locks. Assume nothing. I know a neighbor that had a situation turn very ugly for him in a similar situation. THey wouldn't leave, were dealing drugs from the house and well, they had more rights than he did as a owner/tennant in the same house. Cost him a lot of money and grief.

If they paid you a security deposit which has no paper trail you might have some leverage. Off the record of course... without contracts or leases its difficult to prove anything one way or the other. Which due to Murphys law means they could make it harder on you as long as they occupy the house than you can for them. If they ever signed a lease which has expired and gone month to month... give the deposit back and save the fight for later if its worth pursueing.

In some cases its worth eating it to get rid of them quickly, and without drama. But they should pay in full month incriments... without a written lease or even a prior expired written lease it may be harder to prove but if they were mature adults they would pay the month in full they will be there, even if they leave prior to the end of the month.

Don't let them off the hook on their share of utilities either until those bills arrive and clear. Those can be easy to forget in those circumstances. I've been burned before like that for a substantial amount.

I am not a Lawyer... only commenting on what I have seen directly. Best wishes. I've been in your situation before years ago so I know what its like. It just wasn't in Virginia. Might be worth a few bucks to talk with a lawyer local to you familiar with local ordinances, there can be city specific codes that apply. You need to cover your butt first and foremost. I won't do anything involving more than a few dollars without a contract. Its times like this that show their importance.

Legally no. Without a lease they are a month to month tenancy. This is the law that applies:
Virginia Termination of Lease Notice Law Law Summary and Law Digest (http://lawdigest.uslegal.com/landlord-tenant/lease-termination/5674/)

But being legal doesn't always mean you can stop it. If you have a security deposit, you can use that to cover unpaid rent. Other than that, you will have to file suit to recover what they owe you. You can use small claims court to sue them. You will probably win, but then you will have to collect and that may not be easy.