There is **no way** to make this work. If you *own* both domains, obviously you can redirect one to the other. At that point, however, it is no longer “multiple websites” – it’s *one* website that has several domain names pointing to it.
> I have subdomain like so subdomain.website.com I want to hide the parent directory from the URL
There is no “parent directory” (no “directory” at all) in that URL. If you meant something else, perhaps you could explain further.