Ugh, I feel your pain. Though your housemates make mine suddenly seem like the nicest co-habitors in the world! I've noticed that Male Housemate #1 doesn't clean up due to a kind of childish 'helplessness' about his abilities. To get him to do his share I literally have to talk him through it step by step. "okay, get the water nice and hot. Okay, put in some washing-up liquid, okay, good, now get a sponge..." I'm serious. Occasionally I catch him trying to wash up without getting his hands wet - using a long handled brush and grabbing plates from the surface of the water like they're gonna bite! This is when I wave a pair of rubber gloves under his nose and he looks at them like he's never seen them before.
Male Housemate #2 is a total slob. He doesn't flush the toilet, ever, and quite often will actually miss the toilet in the first place. I never go in the bathroom with bare feet any more. *shudder*
That said, I'm not 100% sure he still lives here, since I haven't seen him in more than a fortnight....
As for Fiona, well, she likes making piles. When she cooks, she leaves her dirty dishes by the sink. But it's okay because "they're in a nice neat pile". That philosophy extends to just about everything. When she left damp washing in the machine for most of a day (while she was sitting in her bedroom) I took it out and piled it neatly on her bed. She looked up at me, amazed and I said "oh it's okay, I put it in a nice neat pile..."
As for advice for you...well, unless you have some way to persuade your landlord to read them the riot act and/or actually kick them out, I suggest moving far far away. If that's not feasible (and I'm guessing not since you would have done it already) then this is the only time I would advocate a PA approach. Put their stuff in their rooms, on their beds. Remove ANYTHING AT ALL from the shared areas that is yours and they use. (This worked for a friend of mine when her housemate decided he would quite like a kettle and a microwave after all.) Don't clean or tidy their things. Just shovel it right out of your way and get on with what you're doing.