"He's not her brother. That's just something people made up"
This could be looked at two ways, with what we know right now. She's telling the truth, and in the new movie they aren't related. Or, she's lying/doesn't really know, and they're related. Trailers are often misleading.
They mention in the trailer that Myers only killed three teenagers so it looks like they're throwing the sibling plot out with Halloween 2.