Cats are a bit more social than some people think. I know that my current cat is solitary, so when we aren’t in the house, she goes bat-shit and has all sorts of separation anxiety and boredom issues. Back in our little cottage in NH, we had similar problems when we only had one, but no problems with three and later five. Long story…
Cats need something to keep them entertained. They prefer something interactive; either prey or another cat—-though the other cat could be prey—to keep them from getting bored, lonely, and loud.
BTW, we had those five cats in a little cottage that was only 20’x20’ with a half-loft for a total of 600 square feet. That is actually a bit smaller than our current two-bedroom apartment. Granted, it helped that those cats were one old cat, two middle-aged sisters, and two young brothers, so in a way it was like having three cats (the siblings got along with each other) but the way I see it, if we could manage five cats in that place, you can mange two even in a place half the size.
Whether the landlord allows that… well, I think that depends on the landlord.