Death certificates can provide you with names of parents. If possible, obtain the death certificates for all children of an ancestor, even though the siblings are not your direct line. Compare the names of parents on the certificates of all siblings.
Mary Cook died of pneumonia in Whippany 10 days apart in 1885. Their death certificates are consecutive. Although they were in their 70s, the informant was able to provide the full names of both parents. This information is consistent on both death certificates.