Liz Buchanan BVSc MRCVS
Hello! I'm not going to lie; this is a difficult, often multifaceted problem. The good news is, that we now know more about feline urinary habits than ever.
The more cats living in a household, the more likely you are to see urinary problems. This is because urination site is a huge contributor to social status and signalling within groups of cats. Cats are not well adapted to social living; even though they form colonies, they don't cooperate much within them in the way that dogs do Eg to sort out territory disagreements. Rather, they will either fight or avoid one another to keep the peace. Urination marks out a cats' territory and within a household each cat tends to have their own separate territory where they can hang out / urinate.
'Inappropriate urination' is often seen when cats are torn between urinating where their humans want them to go, and where they should go to keep the social order as a cat. Cats like to urinate on their own territory but sometimes their territory is squeezed and they go somewhere else, or hold it until they can't any more.
I hear why you don't think this explanation likely, but social standing in a household in the cat world is not the same as having confidence with humans; further, cats outwardly don't show social stress in the way that humans and dogs have evolved to do; rather they have evolved to hide it and one of the main signs of it is indeed inappropriate urination. Cats can look incredibly confident even when they are terrified. It sounds to me that even if they like your room-mate, the new smell us threatening their territory and they are marking against him. This leads to the question why it only started a couple if months ago and I would suggest that this might be to do with some social factor between the cats, or an object left in a different place etc. rather than any big obvious trigger to humans.