Little Monsters by Adrienne Brodeur

 Ken and Abby are the adult children of biologist Adam, a manic-depressive approaching his 70th birthday and trying to ensure his legacy. Their mother died when Abby was a baby, and with their often-distracted father, they had a rather unconventional childhood. Now Abby is an artist and Ken is hoping to run for political office. And though they were very close as kids, they are somewhat estranged now. Into this family dynamic comes Steph--who just found out that Adam is her father too, the result of a drunken one night stand that her mother kept hidden until Steph started trying to track down the source of a hereditary medical condition that no one else in her family seemed to have. It's an interesting character study as Steph meets the members of her bio family without disclosing her relationship with them--then trying to decide whether she wants to be part of this complicated clan at all.