Is it permissible to visit a friend whose father trades in and consumes alcohol? And would accepting hospitality be considered consuming ill-gotten wealth if the father is the one paying the house rent?

The summary of the fatwa is that eating food from someone who deals in unlawful things and whose earnings come from them, such as selling alcohol and usury, is unlawful if all of their wealth is unlawful. If the غالب (majority) or the أكثر (more) of it is unlawful, it is disliked (مكروه), unless the food was purchased with the very unlawful money, in which case it is unlawful. If the unlawful portion is small, there is no harm. The basic principle regarding the food of a Muslim and a People of the Book is permissibility, and one is not required to inquire or investigate its source. Indeed, the Prophet, peace and blessings be upon him, ate from the food of the Jews, and they were people who practiced usury. One should advise those who deal in unlawful matters with wisdom and good counsel.