Messy, but not the same thing as two people living together before marriage. A live-in partner is not the same thing as a family member, even if they are engaged. When two people marry, then they become part of each other’s family through marriage, and through that marriage they may create additional members of the family.
If we uphold the traditional Catholic understanding of marriage, divorce does not dissolve a Sacramental marriage. Upholding that understanding of marriage would eliminate some of the complication for some extended family portraits, but add different complications in cases of divorce with re-marriage outside the Church. When people don’t follow the moral teachings of the Church, life get messy and complicated.