At the risk of being the buzz kill guy, the fact that Jerry's family is involved in the production does necessarily not give me more confidence that the movie will be true to life.
It depends on the family's agenda: is it to push for as much accuracy as possible; is it to make the family and Jerry look as good as possible; is it to settle scores; or other?
To me, it's like the difference between how Aragorn and Faramir were portrayed in the cannonical books versus the films. Tolkien was express that his writing of the LOTR was based on the Hobbits' Red Book of Westmarch. The Hobbits adored both Aragorn and Faramir so it comes as no surprise that the renditions of Aragorn and Faramir in the books are presented uniformly positively.
When Jackson produced the movie - from overseeing the writing of the screenplay to filming the film - he made changes to Aragorn's and Faramir's characters that pissed off many hard core Tolkien fans who viewed the changes as contrary to the cannon. Indeed, the changes were contrary in that Aragorn was presented as a man with real doubts and Faramir a man relatively less quick to follow his better angel.
Being a huge Tolkien fan, I understand 100% why the changes in these two characters' personalities in the films relative to the books angered many true fans. But I appreciated them. Real life humans are simply not as totally perfect as the Hobbits viewed Aragorn and Faramir and as Tolkien therefore presented them in the books. Personally, I found the film characters far more believable and relatable.
So, like I started with, I don't know the family members' agendas. They may be pure: present Jerry as true to to life as possible; or they may not be: whitewash his foibles or, and yes this is possible, too, settle familial scores through the movie (and let's not pretend there is a family on God's great earth with NO such scores).
Personally, I am feeling best about the film, for more than anything else, because the dude directing it is a consumate pro. To quote Wikipedia, "He is the recipient of many accolades, including an Academy Award, three Primetime Emmy Awards, a Grammy Award, four British Academy Film Awards, three Golden Globe Awards, and two Directors Guild of America Awards. Scorsese has received various honors including the AFI Life Achievement Award in 1997, the Kennedy Center Honor in 2007, and the BAFTA Fellowship in 2012. Five of his films have been inducted into the National Film Registry by the Library of Congress as "culturally, historically or aesthetically significant"."
I look forward to the final product.