Anyone over eighteen years of age is required to be on the lease in texas. He needs to fill out an application and apply to live there. Often tenants who have criminal or credit issues will have one person fill out the application and leave the other one off so they get approved. I am not saying that is the case with your tenants but it is very possible. You are protected by your lease and can contact the Austin tenants council as well for help. If she qualifies by herself and he does not you may want to ask him for additional deposit or a co-signer to protect yourself.