How to stop sharing photos

If you want to stop sharing with someone whom you previously shared with --> How to stop sharing your iPhone or iPad content - Apple Support

In the Photos app, go to Albums and then go to Shared Albums. Select a shared album and tap People to see the owner of the shared album and with whom the album is shared. If you’re the album owner, tap the name of a subscriber for the option to remove them. If you’re a subscriber, select Unsubscribe from the bottom of the screen. You can also delete any photos that you shared.