This is a sample message you could use to send to someone threatening legal action
Dear [Ex Member]
Thank you for your email in which you say you are considering taking legal action regarding our local Freegle group.
While I appreciate your concerns, I am not as a local volunteer prepared to respond on legal issues as it could incriminate me. I advise that you contact the administration team of this non-profit organisation at email@example.com where someone with the appropriate knowledge and experience can deal with the matter.
I now will end all communication with you at this time and I have removed your membership to eliminate further potential risk, harm or misunderstanding between ourselves. I take your concerns very seriously and I am sorry that I am not able to act directly in this matter and wish you well.