Rena would probably be Ren. I think Satoko and Satoshi would become Satoru and Satomi (respectively). Rika... Ryo, maybe? I don't know about the others.
Going by alternate pronunciations of kanji in their names: 圭一 = Keiichi -> Tamahi 礼奈 = Reina (a.k.a. Rena) -> unchanged. (actually somewhat of a gender-neutral name; might just go by Ren, as suggested above) 魅音 = Mion -> Mito, Mioto, or Mio 詩音 = Shion -> Utao 沙都子 = Satoko -> Satoshi (yes, I know) 悟史 = Satoshi -> Satoko (again, yes, I know) 梨花 = Rika -> 梨季 = Riki (needed a kanji change, since 花 means 'flower', which is an unquestionably feminine name-ending kanji. "Riki" is spelled with the kanji for "pear tree" and "seasons".) 羽入 = Hanyuu -> Shuuno
