Mr. Pinstripe is a metaphor for Ted's alcohol addiction, and also for his feelings that he doesn't deserve to be Bo's father after killing them both with his drunk driving.
Probably obvious, but yes. Mr. Dickey and Mrs. Birdy are guardian angels sent to help you save Bo and make it through purgatory so you can both go to heaven.
They're the only people around who support you in your quest to save Bo (Happy only helped you to get more of the Fantastic Drug), and once you beat Mr. Pinstripe and get to heaven, you see dolls of them sitting up on a shelf in the bedroom.