Confusion

I just wanted to post this conversation I had with Abbie , or I will forget it...

Abbie "Mom did you know we're actually 'sisters?"
Me "no we aren't I'm your mother
Abbie " No, were sisters and me and taylor, were cousins and sisters... isn't that cool?"
Me "????" at this point I figure she's just being a weird, and I have no idea what she is talking about
Abbie {2 hours later} "and Mom, me and Jack, he's my brother and my sister too"
Me "what????"

And then my mom tells me that in church yesterday they learned that we are all heavenly brother and sisters and that is why at chruch we say "sister so and so" anyway... Miss Abbie didn't quite catch the brother part and she is obviously confused about being sisters with her cousins... but how do I explain it now?? she's so sure of herself?!