What should I do regarding my wife who verbally abuses my parents despite my repeated advice to her?

It is your duty to honor your father and treat him well. It is forbidden for you to obey your wife in matters that involve disobeying your father, because that is one of the gravest sins. Your wife must fear Allah and stop insulting your father, for "insulting a Muslim is فسوق (transgression/disobedience)." Try to advise her not to create a conflict between your fulfilling her rights and your honoring your father.