Hi Aden, I feel for you.... I looked at your listing, (Venice Pied a'Terre), and it looks like you allow 2 people. To only book for one but show up with two people may have been an oversight/simple mistake by whoever booked, so I would let that one go. As for all the extra requests, depending for how long they will stay, I would also just let it go - and learn from it all. I always exchange some extra info with guests before they arrive, that helps in getting to know them a bit and can clear up up some misconceptions they or I might have. Those exchanges ahead of time definitely help me in figuring out if someone is real nice or just barely tolerable....
In any case, best is to speak up right away when you are not happy with something while the guests are there. I also had the "booked for one but showed up with two" scenario last month: it clearly was an oversight, and it was the nicest couple! But another time it definitely was not an innocent oversight: a couple staying for 4 nights, sneaked their young adult daughter in on night 3 and 4, had her sleep on the couch, though my space is clearly listed for only 2 people. I was not amused - but I let it go, and just declined them the next time they requested to stay with us. It's just not worth the aggravation! We can always leave these kind of people a poor review, and we should! Good luck in surviving the bores you have right now...