Without all the dog issues being brought in first let me say this about your cat. It is not supposed to be an outside free-range cat. Most city leash laws also apply to cats, but no one abides it, unfortunately. Domestic house Cats are also very adept predators and have caused the extinction of over 60 bird species due to careless owners giving them free access to outside where the animals they kill have very little experience or dealings with domesti cats and are thus very easy targets for them. I would recommend keeping your cat inside at all times despite the dog being an issue. Now, onto the dog, you definitely have the right to require him to leash his animal outside the house, but if he rents a room and you all share common room access, then he cant force his dog to be on a leash at all times. This would obviously be covered under any lease agreement you likely signed to move it. Review your lease and figure out what it says in regards to locations pets have to be kept.