Earlier quoted context omitted.
Why not take that to its logical conclusion and claim: if he truly never wanted them to be read, he would never have written them in the first place? To me it seems credible that a writer might want to hold on to some drafts, hoping to get round to editing them for publication, but doesn't want them edited by anyone else or published unedited. The question is, how to achieve that, seeing as one can't trust one's heir…
He should have put in his will and testament that all unfinished drafts should be destroyed. I don't believe it is possible to will property to people but put indefinite restrictions on legal usage of the property. I forget the exact term, but the restriction was put in place so that you don't get into a situation where estates are confined to operate in the manner that a long-dead great-great-great-great grandfather…
https://en.wikipedia.org/wiki/Mortmain https://en.wikipedia.org/wiki/Rule_against_perpetuities
There's also the expression "dead hand", but that may also refer to a Soviet strategic defence system, which has also been referred to as "hand from coffin", which is certainly more fun than the official name.