Is the expenditure for the obligatory Hajj of a poor person incumbent upon a father for his son, and upon a son for his father?

A son is not obligated to perform Hajj on behalf of his deceased father unless the father had made a will to that effect, or if the son is financially capable and his father had requested it from him. In this case, the expenditure would fall under the category of dutifulness (birr), which is enjoined.