Copy mode is documented at https://duet3d.dozuki.com/Wiki/ConfiguringMultipleIndependentXcarriagesCartesian#Section_Creating_a_tool_that_uses_more_than_one_carriage_to_print_multiple_copies_of_an_object
Mirror mode is documented at https://forum.duet3d.com/topic/7929/copy-and-mirror-mode-with-idex
I don't know whether printing different models at the same time is supported.