What are the limits of obedience to parents in their commands, such as not wearing sandals to university, and is it obligatory to obey them if they command one to break a voluntary fast?

Obedience to parents has conditions, the most important of which are: that the command is not in disobedience to Allah, that its reason is not foolishness or obstinacy but for a valid purpose, and that it does not result in harm or hardship for the child. These conditions can be applied to matters such as refraining from wearing a specific type of sandal or breaking a voluntary fast.