Is leaving one's father and living with one's wronged mother, who has not been neglectful, considered a sin that warrants punishment in the afterlife, especially if the father disapproves of this choice and stipulates leaving the mother as a condition for his رضا (contentment/approval)?

The mother has the right to refuse to live with the stepmother, and the husband must provide her with a separate residence. As for the custody of young children, it belongs to the mother, while older, discerning children are given the choice to live with either the father or the mother. Therefore, the children have the right to choose to live with their mother, while being keen to honor their father, visit him, and treat him kindly. They should combine honoring both parents with striving to reconcile between them.