Should the father maintain his refusal to allow his son to bring his unlawful wife into the family home?

Marriage is not valid unless the conditions of validity are met: a guardian (wali), a dowry (sadaq), the pronouncement (sigha), the testimony of two just witnesses, and the absence of impediments for both spouses. If these conditions are met, then your son's marriage is valid, whether the girl's lineage is known or unknown, provided she is a Muslim or a chaste Kitabiyyah (woman of the Book). However, if the marriage is lacking one of these conditions, it is invalid, and your son must separate from this woman. It is not permissible for you to shelter them in your home if your son rejects the ruling of Sharia (definition), because that would be considered assisting in sin.