Use of screenshots of Facebook messages as evidence

Dear PAO,

I recently discovered that some of my co-workers have been making derogatory and inappropriate comments about me in their group chat. One of my friends, who was a member of the group chat, sent me screenshots of their conversations. When I confronted them and mentioned my intention to file a case against them, they dismissed my threat, claiming that the screenshots would not be accepted in court because it was an invasion of their right to privacy. Will the screenshots be accepted in court? Did taking a screenshot of their conversation violate their right to privacy?