I'm not sure where to post this.
DD and I met my sister and her family over the Christmas break though we just stayed a few hours and didn't stay over. During this time I did talk to her oldest (SD) who I would describe as a very bright girl. I mentioned casually that my sister (her mom) had banished us from the kitchen and that she seemed grumpy. DN respoded that her parents had had a fight and that her father had hit my sister, but she did not seem bothered by this! I asked about this and all DN said that she had been annoying but she seemed uncomfortable then. She mentioned a few more things along these lines but didn't seem to think anything strange about it. I later asked my sister if she was OK as she seemed unhappy but she said that everything was fine. Since we were alone in the kitchen I told her that I'd heard what had happened, and DS dismissed the whole thing and said they had recently had some trouble with DD telling lies.
I'm not sure what to do now. I only know DN as a very bright, polite and very well behaved child. Admittedly I don't like my BIL much and he has always seemed somewhat controlling to me, but there was nothing to indicate anything worse might be going on. My sister never mentioned anything either, nor did I see any bruises on her but I know that this doesn't mean anything.
My own DD is younger, so I am unsure what to make of DN's words but she has never seemed like a trouble maker (her father is quite strict), so I'd be surprised if she was to make up lies like this? Or am I naive here?