I know this if offbeat but along similar lines....
I recently had to take down a curtain rail that hung over the entrance to the garden of the in law's house. Apparently the rail had been up since before they moved to the property. Anyway on removing the rail I discovered three small crucifixes had been tucked underneath the fixture here and there. The in laws were quite bewildered. I'm still pondering as to whether this was protect the entrance of the doorway from Vampires? And if so the estate agent should had been upfront with them!
^^ from either angle 1) this would have raised the price of the property since it was made vampire-prroof, so better deal for your in laws - or 2) one or both your in laws are vampires and this vampire protection system® could have been a potential hazard (yet it seems utterly ineffective, as your folks don't sleep on the pavement in front of the house because for some crazy unexplainable circumstance they can't get past the garden entrance)
did you keep the crucifixes? you might throw them on the market... seeing economy is low and stuff, maybe better keep 'em in case you fall on hard times
would have been worth your while ebaying them - you know how the internet likes to run with weird stories and chances to buy things at an inflated cost.
Re the whereabouts of the crucifixes, in keeping with the spirit of the season I donned the in law's aloe vera plant with the crucifixes stating that they now had a "tropical xmas tree." Needless to say on my latest visit I discovered that the crucifixes had been taken down and thrown away.