It seems as if it will be important to find out what the master tenant's lease says, if anything, about subletting. For instance, if that lease permits subletting, then the master tenant hasn't violated his or her lease, and the landlord shouldn't be able to evict anyone (not the master tenant, and not you) due to the subletting. If the master tenant's lease prohibits subletting, then the landlord can give the master tenant thirty days to stop subletting, and if he doesn't do so, then he -- and you -- can be evicted, through court process.
Below is a link to a D.C. Court of Appeals case, Young v. District of Columbia, that discusses some of the rights of subtenants.
LEGAL DISCLAIMER Mr. Borbely is licensed to practice law in the District of Columbia. His response in this forum is not legal advice and does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information about the matter in question.
Can you show the landlord knew you were the one paying the rent? If you were directly paying the rent for ten years and the landlord was aware of that, you may no longer be subtenants, you may be tenants. Did you ever request repairs? Did the landlord ever communicate with you directly? Now that the landlord knows you are the ones living there, did they accept February rent? A case may be able to be made that you are tenants.