If he won that much $$$, he needs to do everything through an attorney, particularly with his family....money and sex changes everything in a relationship....His offer to pay off their mortgages and a tidy sum for each, is beyond generous. What they did to him was child abuse.... it should be a one time only offer, take it or leave it. I would sever that tie upon payment, or rejection, and relocate and change numbers or take a different name and ID, but "disappear". The sad story of Lottery winners failing in life and ending up broke is almost the norm... and the people and (Charity?)groups looking for their piece of your $$$ is legendary...hide the money away, invest it, do anything anonymously for donations and only in $500 or $1000 pledges, never more.
His generosity toward his parents...his abusers...is well intended, but will not stop the abuse....and this is some sort of "blood money" guilt payment for his conscience...do it and be done with them, forever.