Nanami and Getou don't live at the apartment! They both have their own places in the city that they stay at, however there is a guest room at the apartment in case someone needs to stay the night. I like to think that while the apartment (on the lower floor) is a "pack space", designed for everyone to gather and spend time together/mix scents, etc. The upper floor is strictly for Gojo/Megumi to have. (Though it's not prohibited for pack members to go upstairs for short periods of time, like how Utahime went upstairs to help Megumi). Gojo's den is off limits of course, and his Special Grade designation has him feeling particularly protective of the second floor as an extension of "core family space".
At the estate each member of the Six Eyes has their own quarters as well, so there are definitely places for Getou to decompress by himself lmao (poor guy NEEDS IT)