Does a young man's shunning of his father's second wife and her daughters—due to her abusive behavior and attempts to alienate his father from his children, and her daughters' inappropriate attire and their traveling without their father—constitute disobedience to his father, who sides with his wife, even though the young man does not fall short in honoring his father?

The right of a father is great, and obeying and honoring him are among the most obligatory duties, while disobeying him is among the greatest major sins. However, obedience is due only in what is permissible. If your boycotting of your stepmother and her daughters is due to their committing unlawful acts, then this is not considered an act of disobedience. But if there is hope for their rectification and their refraining from evil deeds by maintaining ties with them, then it is obligatory for you to obey your father in maintaining ties with them to the extent that it does not harm you. It should be noted that your stepmother's daughters are ajnabiyyat (non-mahram (definition)) to you; it is not permissible for you to be alone with them or shake hands with them, unless they are your sisters through your father or through breastfeeding. You must strive to honor your father and advise him gently and respectfully, and it is not permissible to boycott him or mistreat him.