How do I take down a plagiarized and defamatory website?

This is a pretty messed up situation. My dad is a doctor and he runs a clinic, providing stem cell treatment to cancer patients however due to the controversy of stem cell therapy, there are bound to be some naysayers. We are used to it but there is an issue which has been bothering me for the past 2 years which I've already tried all sorts of channels to no avail so I will like to seek advice and hopefully help over here.

The 4 URLs I have listed below are the malicious defamatory content:…

How do I take down a plagiarized and defamatory website?