Evicting Tenants From Rehab Project - No Lease

Virginia members:

We recently acquired a property for a rehab project that has tenants in it.  I was informed that the tenants were on a month to month lease.  Normally I would serve a 30 day notice to quit in this situation.

Upon further investigation, it seems the tenants are related to the seller, and neither have produced a written lease yet.  This leads me to believe they may not have a month to month lease but an implicit tenancy at will agreement.

While I intend to give them a reasonable amount of time to move, is a 30 day notice still necessary in this situation, or can I just choose a day by which they must vacate the property?  I would appreciate any insight anyone can provide.