I'm a lawyer and cannot give legal advice in this setting. Specific facts change the way courts rule. Only a lawyer, admitted in your state, knowing all the facts can give advice. My specialty is constitutional rights. The flag salute controversy ended with my mom being expelled from high school at fourteen. My brother, who received the highest academic score in the state of New Jersey, was expelled with less than one week to graduation. The Sup. Ct. finally ruled that such laws, applied to parents, were unconstitutional. My father was a drinking buddy of Covington at Bethel.
The First Amendment guarantees only apply to the government, state and federal. Private action is not covered. The Society have a right to enforce their religion. Recently, the Salvation Army purged all non-believers from its employee rolls. The fired employees sued the Salvation Army under discrimination laws and lost big time at the Supreme Court. There is also the problem that you might be viewed as waiving any rights when you became a Witness.
Defamation and libel are possibilties. My hunch from afar is that constitutional rights outstrip statutory or common-law (evolved through judge made law before the advent of active legislatures. Our basic body of law is common-law, except where supplanted by the Constitution or legislation. Actions within the congregation are likely to be lawful. Perhaps billboards or newspaper ads might be a different reason.
Freedom of religion is almost absolute. The only thing that can affect it are neutral laws of general applicability, such as drug laws, not screaming fire in a crowded theatre when no fire is present, bigamy. The law cannot affect religion and must apply to nonreligious people, too.
I don't know how the congregations handle legal matters. Perhaps a letter might chill them. My hunch is that the Society would not kow-tow at all. If anything, the Society seems to disavow its imprint from the actions of local congregations. Most lawyers do free consultations. A single letter should not cost much. The lawyer would hear your dealings with the congregations and obtain a "feel" for how they act.
We faded away. My mother refused to let us be dedicated at the age she was, fourteen. I remember my fervor at that age which soon faded. Outsiders can't truly imagine what disfellowship is like. Witnesses are a very closed society so members typically have few social outlets. My extended family remained active witnesses. I lived in terror of their discovering my activities, Christmas trees, elections, parties, dancing, college, etc. It was so hard to say "God Bless You." Thankfully, they spoke with us. I recommend reading a Bible in complete books and asking what I believed it said. The transition may be hard but the other side is blessed.