Relatives with kids and differences in parenting- when to let things go and when to say something?

I have a 9 month old son and my BIL/SIL have an almost 2 yr old little girl. She is a sweet girl, but you can tell by their parenting styles that she acts out because of them. She still uses a pacifier (which they constantly stick in her mouth!), she runs around screaming if she doesn't get her way. She will hit if she gets mad, kick, etc. Most disturbing is that I've heard them call her a turd and other names! The way we treat our child is completely different. I know he is still young, but it will sit still, even in a restaurant. And we would never call him names, scream at him, etc. Do I mind my own business? What happens when they get older and spend more time together? Has anyone dealt with relatives like this? Did you allow your child to still spend the night and spend time with them? I am just afraid of problems further down the road.