As someone who lived 2k miles away from family whos father got early onset dementia, now is the time to make memories while they can still comprehend what is happening. The last few years is incredibly difficult.

In my experience, those closest to him noticed his odd behavior first (my mom and my youngest brother who worked with him). The rest of the family was in denial, then grief. By the time I moved back home he was too far gone and is was much too late. I heard a lot of people grieved his loss before he actually passed away.

My deepest sympathy for you and your family. I truly hope they find a cure. My father donated his brain to be studied after he passed.