how do I arrange photos chronologically in a shared album in photos

It is not possible to sort a shared album. A shared album is sorted by the date and time you add a photo. It is just a stream of photos, not really an album.

If you want the photos to appear in a specific order you have to share them one-by-one, exactly in the order you want them to appear. if you share several photos at once, the sort order of the selection may not be preserved. Even when you share the photo this way, the sequence of the photos on the public website may change later, when someone adds a comment to the photo.

So, if you want to add a title to the shared photo by adding a comment, add the comment directly when you share this photo, not later.