Potential tenant moving in with her sister

[Ryan Schuler]

My first property (3/2) is ready to rent and I am sifting through applicants. A woman told me that she is interested in moving in with her sister. Both have one child each . They are each going to fill out an application, but should I require that they each make three times the rent or would it be OK if only one of them makes three times the rent? Or If their income combined is five times the rent? What would be the dealbreaker in this scenario? If all things outside of the income are good for both applicants.