The sisters are disenfranchised
With five adult family members, the household should be financially viable, but what the reader sees through Michael's point of view is that, somehow they still do not have enough opportunity between the five of them to have a financially secure household. With finances, money often feels this exact way, that no matter what, the family is always behind. But there is more to this irony—it shows that the sisters are disenfranchised, because only one of them is skillful at a profession that actually fairly employs women. Remember the novel is set in different times.
Michael's sole generation
The five sisters have one formal job between the five of them, and they also only have one child between the five of them. This is ironic, because the sisters all maintain that they are passionate about family. They all talk at length about their desires for love, marriage and child-rearing. Even the one sister with a child, Christina, experiences this romantic frustration. Her child's father will not marry her, although he sometimes seems close to proposing. This irony speaks to their frustration and loneliness.
The missing father turned warrior
For Michael, a father is a kind of legendary animal or something. He does not get to see him often, and when he does, the father is always up to something somewhat unusual or unexpected. This dramatic irony continues to the point where Michael wonders sometimes what his father will end up doing with his life. That is ironic, because typically, the father wonders what the son will do with his life. As a pillar in Michael's understanding of masculine nature, the father is especially revelatory—the father randomly decides he wants to go to war and kill some people.
The ironic missionary
Jack is Michael's other picture of masculine identity. Jack's relationship to the family is strange and scandalous. Some of the sisters believe rumors in town that Jack abandoned his Catholicism and adopted a naturalistic religious mysticism. The irony is potent! The missionary was only abroad to share his religion—not to accept any religious insight. This ironically ethnocentric point of view leads him to a crisis at the end of which, he experiences the opening of his mind and his religious imagination. Ironically, this individualization process makes him incompatible with traditional religion. Michael stands off to the side of this dynamic, trying to piece together what has happened.
Traditional goodness and time
In Jack's case, a moral lesson emerges. The idea of the lesson is simply that perhaps tradition is only half of the equation. Jack's emergence in a foreign, tribal culture leads to his eventual enlightenment, but only when he allows himself to feel that there might be more truth than the Church has taught him. In other words, he embraces change and new growth. Compare that to Kate's staunchly traditional point of view: Kate is focused on maintaining the "holy" status quo, but as Michael admits, this clinging to tradition only sets the family up for a more explosive, dynamic change when time's changing ways catch up to them. Traditional goodness is ironically imbalanced without an equal willingness to change.
