How do I stop the displaying of the image chosen for the gallery page appear on the page that shows the subalbums? I believe it's the album.php page but that is shared by ALL albums in the gallery.

I don't really understand which image you are talking about.

Viewing the Gallery (index.php) page, an image has been assigned to Album 1 which is the parent to 2+ albums.

When clicked one of the subalbums, it takes me to the subalbum page (album.php) where I see the 2+ (not sure how many I'll add yet) subalbums, each with a chosen image.

However, underneath is the one from the Gallery as an extra. When clicked, it goes to image.php for that image . Don't want it at all.