shared album as public website privacy

If you share an album as a public website, everyone who knows the link can access it. So you should only share the link with people you can trust to keep the URL secret. And delete the album again, once all people you invited to the album have saved the photos.

If you can trust the people you send the URL to the chance of someone stumbling upon the website is next to zero. If you look at the UARL you'll see why - it's long and complicated.

If you can't trust them maybe you shouldn't include them in the invite regardless how you set it up.

Just do not send the URL to people who like to gossip or cannot keep a secret, and never share any photo digitally that is very personal. And do not share photos of other people with any third person without their permission. That is independent of the method of sharing.

To share confidential photos selectively, you could mail them. But even then you need to be able to trust the recipients, that they will not distribute the photos further without your permission. You may want to tag your important photos with a copyright notice, for example a watermark.