Carol's family is among those with a type of rare genetic mutation that, if inherited, determines that an individual will develop Alzheimer's with near certainty. This is only true for ~1% of all individuals with Alzheimer's (more here: https://dian.wustl.edu/). For this group, there is very little question about the science. But tragically, we still don't have a cure for them.
But what I expect you are hinting at is also true: for the 99% of other individuals with Alzheimer's, what triggers it, and the role that amyloid plays in that, is a lot less clear. In some of those individuals, genetics leads to higher risk. For others, no genetic links have been found.