1) Litter needs scooping every day. Otherwise cat will rightfully be upset and do poop in the wrong place just to let you know. Recommended to have N+1 litters for the N cats, but small apartment = difficult to place/clean all of them.
2) According to many cat books (notably Jackson Galaxy) litters are a prime scent-soaker and major signpost that lets cat mark their territory. So venting them outside may cause other confidence issues.
Could the smell issue be resolved by simply scooping regularly?