Would I be sinful if I insisted on accompanying my sister on her study trip, knowing that my insistence might prevent her from traveling, especially given my parents' preference for my younger siblings over us?

A father is not permitted to favor some of his children over others in giving gifts, and it is not permissible to harm a sister, based on the Prophet’s (peace be upon him) saying: “There should be no harm nor reciprocating harm.” The sister should be allowed to travel for study if it is good for her, provided she does not need someone to travel with her. One should purify the heart from envy and malice, and remember the words of the Messenger of Allah (peace be upon him): “None of you truly believes until he wishes for his brother what he wishes for himself.”