You are dealing with a highly legalistic organization. Don’t try to beat them at their own game. Just don’t even waste the effort.
It’s tempting to think about walking into an elders room and saying, “Well guys, according to section 3, subsection VI, of chapter 9, <insert legal loophole here>. So based on that, I’m just going to walk away and everyone will be accepting of that decision.” And all the elders turn to one another and go “Ohhh, subsection VI! I totally forgot about that. Yeah, yeah. We’re OK now.”
It was a mistake. You may have been a kid when you were baptized. But it doesn’t matter now. You are an adult, and can decide now to nullify your baptism - “Dear Elders, It has come to my attention that the WTB&TS is full of what some might call bovine excrement. I am no longer a JW. Thanks.”
Your family are also adults and can decide to cut ties with you. That’s a decision they make. Don’t push off their moral agency on something else. It is their, really, their decision. In my case, I confronted my family (kindly) and let them know that it is their decision, and I wouldn’t accept an explanation in which they attempted to shrug that agency off on an organization.
Some shun me, some don’t. Maybe they will come around, maybe they won’t. It is what it is...