How to remove tenant NOT on formal lease

[Ryan McGrath]

Hello BP!  I'm hoping someone can help shed some light on a recent tenant issue I've come across.  

I have a property that I purchased already rented and now some of the existing tenants are having personal issues.

There is a couple living in one of the units, and only one of them is actually on the lease. The person on the lease wants the other person (not on the lease) out. 

Both of them have been living there for years at this point and my question is how do I go about removing the person NOT on the lease? Is that a formal eviction process or is this something that the tenants have to work out themselves?  Apparently, the tenant on the lease called the cops to have the other person removed and the cops said that an eviction needed to be filed.  

I personally have no issues with either tenant.  The tenant on the lease wants me to serve the other tenant a 30 day notice but I am not sure if this is the correct way to go about this.  Also, the tenant on the lease pays the full monthly rent and said that they will not renew if this isn't resolved.