@Danberg,
At this point in your own personal histories, what could it possibly matter?
There are only four ways this can go. None of them are great.
Let's say the answer is yes, and not only are you justified, but he really did perpetrate such deeds. That's horrible. It's also a few decades too late to do too much about it. I doubt you'd have standing to go after him even if there is no Statute of Limitations or there is a window to open up cases decades later, as those windows are generally just for the victims to pursue.
If you're justified but you're wrong, then you're in a position where you've got a hunch but you're just plain incorrect about it. Want to spend the rest of your years feeling guilty about jumping to conclusions and being overly judgmental? Knock yourself out.
Or maybe you're not justified, yet he did the deeds. Again, the (probably) only person who could go after him legally is the younger daughter. Which she may or may not want to do at this time in her life. Unless she is utterly incompetent, she will have a say in whether to bother pressing charges now. Inserting yourself into the middle of that is unlikely to provide any positives for you or benefits for her.
Or maybe you're not justified, and he's innocent.
Not every question we have in life has to be answered.