My guess is Rob Reiner left Nick out of his will. The kid is flat broke.
California, like most states, has a “slayer” provision in its probate code that says a kid who kills his or her parents gets nothing even if named in the will. I think you’re right that the withdrawal was due to an inability to get paid, which is supported by the fact that a public defender was appointed. Brother and sister are probably not inclined to help with the defense of the guy who killed their parents.
The California law won’t let him collect on any inheritance being that he murdered the one leaving him the money.
If Nick Reiner is convicted of murdering his parents, he will be ineligible to inherit from their estate due to California’s “Slayer Statute,” which prevents a murderer from benefiting from the victim’s estate. This law applies even if he is not convicted, as long as it can be proven that he intentionally killed them.