My parents are lenient on some clear matters in the religion. They're considering sending my sister alone to a university in a kafir country. I've encouraged a local university option, but they've asked me to stay out of it. What are my responsibilities to avoid sin while honoring my parents?

A woman does not travel without a mahram, as per the hadith, and the people of ilm first ask whether the study itself is a necessity, more so in a kafir country. Advising parents with gentleness and good adab is not uquq, and obedience to parents is in the permissible and not in sin. Once a person has advised, he has delivered what was upon him, and no one is held accountable beyond his ability or outside his authority.