Is it permissible to recite the Qur’an at a funeral, and is it permissible to customarily complete a recitation of the entire Qur’an for the deceased after three days, even if they were disobedient?

Reciting the Quran at a funeral is not permissible if it is done as a Sunnah, due to the lack of evidence for it in the Sunnah. There is no difference in this regard between a righteous or an unrighteous deceased person. The Quran must be recited with tartil (slow, melodious recitation) by whoever is able.