Which is more prioritized: paying off the father's debt and assisting him financially, or fulfilling the needs of one's family (wife and children) first, especially given financial hardship and its impact on family stability?

Supporting poor parents is obligatory for the capable child, provided it exceeds his own expenses and the expenses of his dependents; for the family's expenses take precedence over the parents' expenses in case of conflict.

As for the father's debt, the son is not obligated to pay it, but it is recommended to pay it if circumstances permit, as this is an act of filial piety.

If it is possible to combine buying a car and paying off the parents' debts, that is better. Otherwise, buying the car is prioritized to meet needs and earn a livelihood.