Taking the legal route will not yield much. This doesnโt mean you shouldnโt confront him. Take help of other family members you trust and confront him.
Note that since this is really old, there will be a lot of melodrama. He might deny it completely, many family members might not support you or disbelieve you. There will be consequences to this disclosure that will be unpleasant and gut wrenching. So when you do this, make sure you have the stomach for it. Donโt flake out midway because then you will be worse off.