Evicting/Removing Third Party "Squatters"

[Mark Douglas]

Upon the purchase of a rental, I inherited a tenant.  The lease agreement only has this person's name on it.  I had this person sign a new lease with me.  The person on the lease has two or three people living in the unit at any given time.  I didn't necessarily have a problem with it, the tenant was paying rent, and there didn't seem to be any issue with the other people staying there.  

Now it seems that my tenant is having some pretty substantial personal problems with these people, but for whatever reason, continues to let them stay. 

Is there any recourse that I have, against these other people?  They aren't on the lease, but they are certainly "dwelling" there.  I don't want to evict my original tenant since there aren't any problems there, but these other people are giving my tenant major problems, which in turn are giving me problems.