Would family members of a suicide victim blatantly lie to others about cause of death? In my (slightly biased) opinion, Millard flat out lying and saying WM died of a brain aneurysm rather than being honest speaks to his guilt. Perhaps there are other reason that a family member would flat out lie? I can see wanting privacy and maybe struggling with the stigma of suicide by staying quiet or not giving details, but flat out lying seems to be a bigger step than I would expect.
I think you may have answered your own question. The stigma of suicide is profound and if you couple that with cultural positions and religious edicts against suicide you have a perfect storm for why some families may choose to lie and come up with a more acceptable mode of death. I'm guessing that while lying may be seen as wrong, the shame and stigma of a family suicide may be worse. I, of course, am in no way applying that line of thinking to DM....my position is very much that he murdered his father in a premeditated fashion and lied for the obvious reason. As an additional thought, I can almost see DM in his own twisted way laughing to himself as he told people his Dad died of a brain hemorrhage because that IS EXACTLY how he died. Clearly without elaborating on how his father's brain came to hemorrhage.