Is obedience to parents obligatory if they command a recommended act, such as fasting on Mondays and Thursdays, or performing Duha and Witr prayers?

A child must obey his parents in what is good. So, if they command something that does not involve disobedience to Allah and no harm to the child, and it benefits them, then obedience is obligatory. However, if they command a supererogatory act of worship, such as a voluntary prayer or a voluntary fast, obedience is not obligatory. Nevertheless, the desirability of such an act is emphasized due to their command.