First, call or visit your county courthouse. They may have some 'self-help' brochures that will explain the process and the local law in this regard. Second, if you have a lease, read it carefully. A lease is a contract and, as long as it is in compliance with the law, it can be enforced. Third, you may want to consider talking to a lawyer. It will cost you a little bit of money, but in the long run it may save you a ton of money in lost rent
I am a landlord myself here in New Jersey. It's not easy, but then again I have never found a way to earn money for nothing. :) In the future, I would try to avoid renting to family members. It's just too close an emotional tie. Leasing a property is a business transaction and should be treated like one. If you were a doctor or a lawyer you would be advised not to treat or represent yourself or your immediate family and that is good advice for landlords too.
Going forward, make sure you verify employment, do a credit check to make sure the potential tenant pays their bills on time (they don't necessarily need a stellar credit score, but they do need to have a history of paying their bills) and get references. You may even want to get a criminal back ground check. You can never be too careful