Is it Islamically permissible to expose the academic plagiarism in a book co-authored by two colleagues, even if it causes them moral harm, given that the plagiarism is 100% proven?

The actions of the two individuals mentioned involve two prohibitions:

First: Infringing upon the material and moral rights of authors. The ruling on this and its evidence have been previously explained.

Second: Deception and pretending to have knowledge by attributing what is written to oneself when it is not so. The Shari'ah has forbidden deception, as the Messenger of Allah, peace and blessings be upon him, said: "Whoever deceives us is not of us," and "The one who pretends to have been given what he has not been given is like one who wears two garments of falsehood." And whoever attributes something to himself that he did not do falls under this hadith. He is the first to be harmed by this, as he accepts people's praise for an action he did not perform, and he abandons the serious pursuit of knowledge.

And whoever becomes aware of this matter should advise the perpetrators to fear Allah and clarify the matter to people as a warning and deterrence.