"To be honest, I don't think there was much of an agreement."

You stated, "they did it themselves on Legalzoom." Did what? You cannot state there is not much of an agreement, then pull up the Secretary of State website where they filed the LLC paperwork and are running this under an entity.

That's why the reference to a lawyer keeps coming up. They can't make an initial mess, then try to walk away to their tax benefit, and expect either process to be the right legal process.

And you mention goodwill. That implies someone sold something, they bought that something, and everyone is supposed to agree on what was purchased and by value. So that other party also has some evidence that something was in fact in place and is much of an agreement.