Is there a nice way to "butt into" a family member's parenting practices?

I completely disagree with my sister's parenting. She doesn't actually discipline her children. She just yells at them. They don't have any bedtime routine at all. They only take baths every 3 or 4 days, sleep in their clothes. They average fast food 2 meals per day with sugary cereal for the third meal. BUT I think she honestly loves them in her own way.

The problem is that I truly think that the way she is raising the kids will be harmful to them, both today and in the future. So I'm torn between feeling like I should say something to her for the sake of her children, or could I be causing more grief in the long run? She tends to try to prove people wrong when they disagree with her. I have tried "modeling" good parenting techniques when I'm around them, but that doesn't seem to do any good. I just don't know what I should do...