I suspect the threat of litigation will be dropped now that Erin has taken down the review and once he puts up a revised one with the feet.
Nevertheless, I agree with
@amirm that they shouldn't be threatening legal action at all, at least not before reaching out to Erin more amicably to see if he'd be willing to dialogue and work with them (which he no doubt would have). And I agree that raising money for a separate legal fund distinct from Patreon would be much more effective in sending the desired message.
Perhaps the simplest method would be a GoFundMe page, though I'm not personally versed in setting one of those up. I'd certainly donate.
Where I live (Canada.) to sue somebody one needs to go to a informal hearing with a judge and explain the details to the judge. Then that judge decides right there if the litigation has merit. A lawyer may appear for both parties for that meeting but is not required. Nor is a lawyer required for the actual court proceedings because the judge will advise/act as council for the two parties if they need council. Any idea how it works stateside?
This up-front process exists in some US states for certain kinds of lawsuits, but it's very hit or miss depending on what state the suit is filed in and what kind of claim the plaintiff makes.
In general, the problem in the US is that it's hard to win a bogus lawsuit, but it's extremely easy to
file one, and inescapably expensive to defend against one.