Automatically fill-in or adjust the parent Item start/end date columns based on the earliest and latest date for the relevant subitems.
The app Rollup Subitems can do that. To define which subitems are relevant you can use filtering. Thereby the earliest and latest date of ONLY the relevant subitems will be put in the parent item (in a real monday column, not a mirror).
Thanks, Bas. Our company is not currently reviewing or allowing additional apps, so we really need native solutions.