Worrisome childhood trend in family of bipolar/NPD

[Washisheart]

My friend's bf is diagnosed bipolar & has NPD traits.

His little cousin slept over their house and wet the bed. She is 10 years old! And his response was that "it's no big deal, everyone in my family wets the bed late" and proceeded to say his sister was 14 years old.  Now I don't know his entire family, but more than enough members to let me know, its not a genetic trait, there is physical, emotional, and now I am bound to think sexual abuse behind it.

Is there even a way to approach the topic of having a heart to heart with that little girl to him?