Luna probably isn’t even human. I get a feeling she is a project from DOATEC or something lol
I bet Misaki is an idol & Tamaki is her sister & fashion designer or something like that
Well, Ayane does seem to speculate that she's an alien, though her remark that Luna has a sense of humor seems to imply she doesn't actually believe her own theory.
I'm not sure she's a DOATEC experiment, though. That just gets into Resident Evil-type storylines, and quite frankly, after the crap from RE7 and MGSV, it's a better idea to not introduce something like that. Leave it to Kasumi clones. She's probably an eccentric human.
As far as Tamaki, we don't know what her relationship to Misaki is. We only know she's an older sister type figure (the Japanese are very loose regarding familial terms, meaning they don't necessarily limit it to those related by blood, or even those adopted for that matter).