I think that it was difficult for Lee to have Jackie as an elder sister, because whatever Lee did, she could never catch up with Jackie's achievements. The question is certainly right in that the effect of Jackie marrying Onassis was not good for their relationship. Although Lee did conceal what it meant to her, I think she suffered a good deal from it. I don't know what Gore Vidal said to Hillary Clinton. I understand she did some paintings, but have never seen any.
Paintings are sort of a window to the soul.
Yes, I have seen paintings by Jackie. They're Jackie in her little-girl mode. Regarding the journal, I have to say I do not know. The Manchester tapes, about the assassination, are embargoed until 2067. I imagine the Schlesinger tapes are also embargoed at least until that date.