In this context, the term "wholesome" is likely used with a bit of irony or contrast. The description highlights the unconventional appearance of the Dauntless families (piercings, tattoos, purple hair), which traditionally might not align with the typical image of a "wholesome family unit." Generally, "wholesome" refers to something that promotes good health or morality, often associated with a conventional, traditional, or family-oriented image.
The irony here is in juxtaposing the non-traditional, perhaps rebellious, appearance of the Dauntless families with the term "wholesome." It suggests that despite their unconventional appearance, these families still embody the core values of a family unit, such as love, support, and togetherness. The author is possibly challenging the stereotypical image of what constitutes a wholesome family.