Yuki and Towa are secret loversThey managed to keep their relationship a secret from everybody, including the band members. Yuki and Towa's relationship with women are just a cover. Check the anime:
Sakuya's mother was not fully Japanese, and neither is AineBlue eyes are a recessive trait compared to brown eyes, but if both parents carry the allele for blue eyes, there is a 25 percent chance that the child will have blue eyes. Unknown to them, both Reiko and Aine have European ancestry somewhere down the family tree, which would explain how their sons have blue instead of brown eyes.