John’s nearest relatives in the novel include his cousins, Simon, Noah and Hester Eastman. Hester influences the lives of both boys. Of course, she is close to John since they are related. Although she is not related to Owen, she eventually becomes his lover and they care deeply for one another.
Reverend Louis Merrill also has an impact on both boys. Owen attends the church services, where the Reverend presides, without his parents who do not worship with him. He is attentive during the services and has a deeply religious view of his purpose in life. However, John’s life is most profoundly affected by Reverend Merrill. After years of searching for his biological father, John discovers that the Reverend is his lost parent.
Without question, Tabitha Wheelwright most impacts John and Owen. Owen initially admires her with child-like infatuation. He adores her and treasures the love and attention that she shows to him as her son’s best friend. Moreover, her death as a result of his ill-fated foul ball changes his life course forever. John, too, is changed forever when he loses a mother who has cared for him and loved him. Tabitha Wheelwright was the most important person in the lives of both boys.
In an odd sort of way, Mr. and Mrs. Meany impact both Owen and John - Owen, because of what John later calls their "ignorance" in telling him of his "virgin birth," and John, due to the puzzling lack of involvement in both Owen's and John's lives.
As well, John's aunt and uncle in Sawyer Depot impact the both of them - John, for the obvious reasons; Owen, for the troubling lack of never having invited him to spend time there with John (until late in the story).
While I am aware that these two examples are a bit quirky, and perhaps the most of minor of minor characters, I think Irving enjoys the quirky voids that seem to be mentioned in passing, but hold more significance than may meet the reader's eye upon first glance.