Yuki is Tatsuha's older brother, the two may look alike from the outside, but they're opposites when it comes to personality. Tatsuha likes fun and excitment, while Yuki is mostly always grim, quiet and calm. Tatsuha pretty much acts his age though. XD The two have a mutual feeling about one another, Yuki finds Tatsuha annoying at times, but most of the time the two don't get screen time together. Tatsuha finds Yuki a bit too grim for his taste, but he more or less respects his older brother.

Mika is Tatsuha's older sister, the two don't have much screen time together either. They never spoke to each other in the anime, and Mika doesn't appear in the OAV series. Since Tatsuha is care-free, I'd imagine he's not around the temple too much, and doesn't come in contact with Mika much.

Tatsuha's dad runs a temple and is a monk. Tatsuha is always running errands for him, such as getting Ayaka and Yuki to come back and bringing Ayaka to Yuki. He doesn't seem to get into much trouble, his father's main worry is Ayaka and Yuki's relationship anyway. Tatsuha probably spends some time at the temple, but Mika is really the only one that their father can count on. XD