According to the 18 sources I have identified (see Nellie Helper Olender in familysearch.org), Nellie was not a sister to William, Isaac, Samuel, and Julius. She was likely a niece of Issac's wife Brucha Birdie Helper. She lived with Isaac's family in the 1900 census. I've listed Nellie as a child of Issac's in family search.org and also have her husband and children listed. These sources match the clues from Irving Olender's research. If anyone has more information or insight into this, please let me know.
Eric Olender
