Sayuri are relatives but but not close ones.
1. Riku and Kana are different entities. Riho and Kiyomi are different. I'm yet to think about making her appear.
2. Yes that's her grandmother. HQ stand for headquaters. No name given to her since she is not gonna appear in Magic Ring.
Mariko and Ame are not related.
That's her uncle.
Different Mikasa's from different universes like Mauso. Mikano from Ravaging beast and Mikata from Street Hound. They are not important as there only interaction in the game are as ghosts.
Mei family line has changed a lot. At first she was Masuo's mom's friend therefore her surname was Nakayama in original Magic Ring documents. Just forget to change that when she was included in poker game.
People are going to refer to your documents so it's fine asking question as it would make more accurate character list.
Also I thought you might have already datamined her from game files. Nobuko Ishida.
