How to bring it up
You’re going to have to pretend to see where his family might be coming from, even if you don’t. In essence, you have to start by making excuses for them. You could say, “I realize that they come from this background, or this culture, and so x,y or z could be the reason it seems totally normal for them to act this way.” At least show you’ve tried to see their side of things, so your partner doesn’t think you just see his family as bad people. Then say, “But it makes me uncomfortable when they…” The point is how it makes you feel, not how you’re judging his family’s behavior. Nobody knows how to handle his family better than your man does. If he cares about you, he will handle it from there.