Is not accompanying one's parents for Hajj, due to a conflict with a new work project, considered disobedience (ʿUqūq) and a violation of Islamic law, especially since I have performed Hajj before and they have performed it multiple times?

There is no harm in apologizing to one's parents for not taking them for Hajj if they have already performed it multiple times. The apology should be delivered with wisdom and gentleness, accompanied by a suggestion to spend the Hajj expenses on charitable causes, such as sponsoring an orphan or a needy person, or assisting someone in need. This might be better than performing a supererogatory Hajj. Apologize to them gracefully and do not spoil the project [of earning a livelihood] in order to save for yourself and your children, and to maintain your dignity from having to ask people for help; that is better for you.