Oh, okay. I see. Everything that happened in the second half of the first episode makes more sense now. Sasami’s brother holds the power of Amaterasu, a major deity of Shinto religion. God(dess) of the sun (and whole universe, apparently) who commands all other gods. And because Amaterasu is in Kamiomi, everything bends to match his view of the world… whether he’s consciously aware… I don’t know. Doesn’t look like it.
That’s also the reason why Sasami has him under surveillance twenty four hours a day.
Next is to know who the Yagami sisters really are… going by the god theme, I’m guessing Onmyouji.
Their surname is 邪神 which literally means evil god.
Hope that doesn’t count as a spoiler…
The sisters’ names are Sword, Mirror and Sphere. I didn’t get that until the second episode, when they were said one right after another. So, maybe they’re like personified magical items?