I guess all we can do is go by our own experience, but I've had cats my whole life, and there has never been a problem integrating them into my household. This includes my adult life (single and married) mostly in smaller condos and townhomes, and we never let cats outside, so they're forced to get along!
I think the biggest mistake people make is they expect too much, too soon. I recently moved temporarily to my sis's and I have a large Yorkie (11 lbs) and 2 cats. My sis has a medium sized dog and a large one. So we've got 5 animals! There have been minor adjustments, especially since at least one of the dogs had never been exposed to cats. But all 5 are socialized and well treated, so it's working out.
Short version: I think this will be fine. In fact, it sounds like fun and will likely take pressure off your 18 year old.