Saving site by converting to static HTML

A couple of years back I helped my brother and his wife setting up a simple WordPress site for their wedding. Now I would like to download the complete site as standalone HTML-pages and save it for them for the future, but the wordpress functionality is no longer needed.

I’ve looked at the plugin Duplicator which can save everything in a zip-file, but the files will still need a WordPress installation to present the pages – and who knows how long this saved copy will remain compatible with newer versions of WordPress.

I’ve tried the plugin WP Static HTML Output, but it just returned a number of files containing ads for “adult entertainment”.

I’ve tried the plugin Really Static but it didn’t return any files at all.

I’ve also thought about finding if there are any “site ripper” programs that I could use, but I know of none.

So… I’m looking for any advice or suggestions of ways to do this.