I found Judy's father to be a calm and reasonable influence. He seemed to be a critical part of Judy's life. Do you agree? Or was he merely a spectator with little effect on the story?

I think Judy's father was a rock solid guy who was always trying to do the right thing. His constant and unwavering attention to Judy's care and upbringing made me admire him very much. He remained single for most of Judy's young life which I also found admirable but was strong enough to become involved when he felt it was right for him and do all he could to make sure Judy was not threatened by that. He handled every situation with equanimity and kindness.

He was the rock in her life. A very caring and loving role model.

Kirk was and will continue to be THE most important adult figure in Judy's life, the principle adult influencing her development. He modeled being a productive/contributing member of society through his education and career. In a more personal way he consistently cared for her everyday needs. Most significantly he truly loved and nurtured her.
On the negative side he was an enabler in Cassie's life and thus HER affect in Judy's life. The author introduced us to Kirk's enabling on page one with his acceptance of Cassie's substance abuse during her pregnancy and his signing Judy's birth certificate with the ridiculous name "Sweet Judy Blue Eyes." This enabling continued through Cassie's drastic choice of moving to the commune until Kirk appropriately involved the police. Kirk maintained his role as an enabler by allowing Cassie to come in and out of Judy's life - even allowing her, after her membership in The People's Temple, to not just stay at their home, but also in his bed. Kirk suffered personally by his continued ties with Cassie preventing him from having an intimate relationship with another woman (until years later with Treva). Strongly disagree with joyces (and responses to other threads) that Kirk's single status was a constructive choice for him or Judy - not because Judy needed a "mother figure," but rather that Kirk needed to to experience and model a healthy male/female relationship.
Please note that Cassie and Kirk had much different personalities than Cassie's parents, yet they still had the same dominant/passive relationship as them - Cassie's choices controlled their relationship, while Kirk's life centered on responding to those choices.