Drug laws

I've looked online and can't seem to find anything on it. but I have myself a situation.

my husband's niece and her boyfriend are staying in our house unexpectedly. and it has came to my attention that they are getting high. im pretty sure it's heroin or possibly coke. they won't admit it and my husband won't put them out. I'm afraid if it comes to it and I have to call the police I'll get in trouble since I own the house. but I don't know how to get them out any other way.

does anyone have any experience ? I've never really been around drugs and don't know what to do