Guest never leaves the house

I have a guest and her husband book our basement suite for 1 week. They extended for 1.5 months more

They are from another city that is a 3 hour plane ride away

They literally stay inside all day. Many days they don’t even open the door once

My concern is if they may turn out to be squatters. I assumed when they flew here and extended their stay to 2 months , they had obligations here. If they work from home, they could do that in their own city. There wouldn’t be a reason to travel across country to work from home and literally never come out

I know some comments will say I should mind my own business. Regardless, it’s a curiosity that I can’t figure out. Again, my concern is that they may not leave on check out since their is no apparent reason for them to be here for 2 months