Hello,

Regarding ligthbox web part, there is 'filter out duplicate items' property in its configuration. Could you please make sure it's set to false?

Regarding related documents, regrettably linked documents have different NodeGUID than original document and relationship is defined based on NodeGUID so the relationship of document doesn't take effect on linked document. You will need to specify relationship for linked document apart.

Best Regards,

Martin Dobsicek