How do I add additional tenant & rent increase to the lease

[Vy Mai]

I just found out another person is living on the property without my knowledge... I confronted the tenants and they said they like to add the new person on the lease. My question is:

1. Do I have them all start signing a new lease or just do an addendum ?

2. How do I put in an increase in rent?

Or... what do you guys do when this happen to you?

Thanks!