Tenant doesn’t live in house
To my surprise, after 8 months I found out last week that the 2 people who signed the lease do not live there. Their daughter lives in the house with her boyfriend. I’ve never felt the need to just drop by unannounced as I’ve never had any issues. The few times that I have ever entered the property I have given them 24 hours notice. When I go there I meet the lady who signed the lease.
Last week there was a plumbing issue (toilet backed up and overflowed ) with minor damages. I proceeded to tell them that they are responsible for it and that set them off. During all this the neighbor whom I’ve known for four years told me who was actually living there. I kindly ask them to leave since they were in violation of the lease terms. 
Has anyone ever had to prove that people were or were not living in a property? if so, how did you do it?
(I’ve already checked county records and they have a house in their name)
Thanks