how to preserve order in a shared album

The most reliable (and time consuming) way is to add the pictures to the shared album one at a time in the order you wish them to appear in the shared album.

When you go the trouble to arrange the photos manually by adding them one-by-one, I would not allow the subscribers to add their own photos or to comment on the photos. I noticed that the order by the date-added in the Shared albums may change, when I add a comment to the photos. The photo with the new comment has been moved to the end of the album, when I viewed the shared album on a different device or on the public web page.

You may have noticed, the titles and captions are also not shared. We are still seeing the titles and captions and locations when we are viewing the shared album from the Photos Library where we have shared the photos from, but when I view the Shared album in Photos on one of my other devices the titles and captions and locations are missing. So we have to add the necessary metadata as comments. To avoid that the photos might get rearranged when adding comments, it would be best to add the comment for each photo as soon as we share the photo. And we should wait with inviting subscribers until all photos have been shared. Otherwise the subscribers might receive alerts for each photo we share, which could become tedious.

Thank you for the solution of adding one by one.

I concur on the time consuming comment, especially on an iPad or iPhone without a mouse. Having a shared SequenceNumber attribute for the shared album would be great and facilitate reordering. Photo albums created from the timestamp a picture was taken don’t always tell the same story. Airdropping or messaging just adds burden to the recipient too.

Thank you! Time consuming, but at least it worked. How disappointing that Apple doesn't provide a better solution.