Tenant wants to add a roommate

[Albert George]

I have a existing tenant who wants to add a roommate. How do I go about. 

I assume I will have to qualify the roommate on the same terms as the tenant. Should the roommate also qualify individually for the 3+ income requirement?

Should i include the room mate into the current lease document that I have with the tenant. Or sign a completely new lease with the roommate?

Can I have two lease documents on the same property?