Since her father is ADOS she's probably less then half black. AA tend to have 20% of european in them on average. Halsey may fall under the 80%-90% European range.Yes, they would.
White people in this day and age primarily go for appearance. No one looks at Halsey and thinks she's mixed. She's literally half black. The grandchildren of black men who are 75% white and look it, will most definitely gravitate towards their white side and their white ancestors will be nothing but a footnote in history. Also, 'passing' is a thing amongst cadaans. Pale madows used to routinely move to different areas, marry cadaans and pretend to be fully white. That is why you have a many many cadaans that have significant amount of madow blood.
Cadaans rarely have any madow blood in them, on average Cadaans are 98%-99% European while that 2% or 0.1% is either west african or Native american