If, in fact, the landlord has regained possession, then it may be too late to fight the issue. At the time that there was no lease, the arrangement became a month-to-month. That was the best time to request a renewal of the written lease. The question is whether the mother-in-law had the authority to bind all the occupants of the property, and it may be construed that she did if she was making rent payments or had other direct dealings with the landlord.
In a manner of speaking, as there was no written lease since July 2011, there cannot be any reliance on the lease of July 2010 as it expired on its own terms and the occupants were vulnerable to a termination of the arrangement at any time upon proper notice--usually 30 days.
The information provided here should not be construed to be formal legal advice. The provision of this general advice does not create a lawyer-client relationship. Persons with legal questions are encouraged to seek independent counsel for advice regarding their individual legal issues.