Tenant with live in boyfriend (and dog)

[Carrie Pledger]

I have a tenant whose boyfriend is essentially living there now.  The lease states that no one can stay more than 15 days without being on the lease.  She says he stays at his own place about once every 10 days (conveniently, to get around the 15 day limit).  It has been going on for a few months but I've waited a bit to see if she would tell me.  She seems to also have other people and pets staying off and on.  I want to make sure I'm not starting a pattern of leniency but I am not sure what action is in my best interest.  Would you make the boyfriend sign the lease or would that cause more problems for me later?  I'm thinking about requiring an extra security deposit and $25 monthly fee for the extra dog he brings.  Here is what the lease actually states:

Guest(s) staying over 15 days without the written consent of OWNER shall be considered a breach of this agreement. ONLY the following individuals and/or animals, AND NO OTHERS shall occupy the subject residence for more than 15 days unless the expressed written consent of OWNER obtained in advance .