These ID numbers are only available in databases with this feature in crawl.
These are DISCO-generated identification numbers that can be added to your custom view to help you understand the composition of the families in your document list.
The family ID is shared by all members of a family and is always equal to the document ID of the family’s head parent.
The parent ID is only populated for attachments and will tell you the document ID of the attachment’s parent.
The attachment ID is populated for parent documents and will enumerate all of the document IDs of the immediate children attached to the parent.
When a reviewer downloads a document list export, all metadata will be included in the list including the family ID, parent ID, and attachment ID for each document. This is especially useful if you wish to keep families together when doing data analysis outside of DISCO, e.g. in Excel.