It seems to me that the first thing the LW needs to do is to sit down and discuss with her BF how she feels, how his family's behaviour affected her and how she felt about the extent to which he 'warned' her.
Whether he is willing to discuss it, and how he responds when they do would be big factors, for me, in deciding whether I felt that this was something which our relationship could weather.
BF's views and actions may well be very different from those of his family, but if the couple stay together, there are going to be issues around whether they spend a lot of time with these people, whether they are willing to entertain them in their home, what contact they would be willing for them to have with any children, in the future etc. I don't think LW and her BF need to be able to decide all of those issues now, but I think they do need to be able to discuss them, and to get some idea of how far apart they are in their views.
If BF's view is that family is family, and if they behave in ways you don't like, you just grin and bear it, but you don't challenge them and you don't restrict your interactions with them, and LW's view is that you do't have anything to do with people who behave like this, then you can see that there are massive problems ahead. Better to stat addressing the issue now, than when you've committed to a joint home, moved to accommodate a partner's job etc.
It may be that LW will find that BF was 'unapologetic' because he was embarrassed and defensive, and that he found his relations worse than he remembered them, seeing them with new eyes after having been away. If this is the case, then a calmer, non-judgmental discussion (non-judgmental of him, I mean, not of the family's behaviour) may allow him to become less defensivve and better able to think about the concerns raised by LW.