Based on the details provided, Ronald DeFeo Jr. should primarily be charged with 1st Degree Murder (option a).
1st Degree Murder usually involves a premeditated intent to kill. Although you mention that he did not plan the murders, the fact that he intentionally shot and killed six family members suggests a conscious decision to commit the acts, even if he was under the influence of drugs and experiencing hallucinations.
In some jurisdictions, his ability to distinguish right from wrong might be explored in terms of a defense against 1st Degree Murder, which could lead to a discussion of mental health evaluations. However, given the nature of the crime and the number of victims, it aligns closely with 1st Degree Murder.
Other options such as 2nd Degree Murder, Voluntary Manslaughter, and Involuntary Manslaughter may not appropriately characterize the severity and circumstances of his actions in this case.