It depends on how complicated you want things to become. If you want to stay within the Lightroom system, only Lightroom Classic and the Lightroom (cloudy) desktop app allow the capture date to be changed.
For Classic you would have to export the images as a catalog and send the exported catalog to your father. In theory, you don't need to include the negatives in that catalog transfer, provided you ensure that library previews ARE included. On receipt, your father would need (obviously) to have Classic installed, but if he hasn't got a current subscription he could download and use the Classic trial and off he goes. The only issue is whether or not he could edit the capture date when the original images are "missing" (as they would be if you sent only previews), though it may be possible as initially it's only a catalog change and the image itself isn't changed until you save metadata to XMP, which you could do when you eventually merge the catalog back into your master catalog.
For the Lightroom desktop app, the best solution would be to allow your father access to your Adobe ID, which would allow him to install the Creative Cloud desktop app, which in turn would allow him to install Lightroom. In the meantime you would still have to sync the collection of the scans to the cloud, which he would then automatically get access to when he installs Lightroom. He makes the caption changes there, and can edit the Capture Date as well, which would sync back to your Classic catalog, after which saving metadata to XMP should also change the capture date in the file instead of only in the catalog.
There would be probably be off-Lightroom options (Bridge comes to mind), but I'm not overly familiar with those.