The new power couple? Sisters (see: Kate and Pippa; Dakota and Elle; Mary-Kate and Ashley, and that third Olsen chick).Add Mikha Diaz and Mary Elliott to the list. They’re the creators of the very original Two Sisters Bar and Books, a bar-slash-book lounge opening Friday in Hayes Valley.The long, cozy space resembles an old-school gentleman’s library, with burgundy and mustard wallpaper, velvet drapes, and bentwood chairs.Perch at the marble counter for prime people-watching, affordable bites of nostalgic Americana (savory bread pudding, chicken meatballs), and locally sourced wine and beer (classic cocktails coming soon). Fixed-price brunch involves coffee or tea, something alcoholic, and an entree for $20.You may also notice books everywhere. Brooklyn, New York-based Elliott sources readable volumes that will rotate constantly with a take-one, leave-one policy.Because siblings share.Two Sisters Bar and Books, 579 Hayes Street, between Laguna and Octavia Streets (415-863-3655 or 2sistersbarandbooks.com). Mention DailyCandy in October for a free glass of bubbly.