"no overnight guests, no cursing and no sinning" guaranteed!
Bold claims since in the eyes of God we are all sinners and no one is without sin, even you.
As long as you make sure you are doing the right thing - no overnight guests, no cursing and trying to minimize your sinning - you needn't worry about unclean spirits whatever they are.
Perhaps your landlord is allowing the couple to stay as an act of love to her fellow man and helping them out in a hard situation and following the scripture In Matthew 7:1 and not judging them.