In thousands of years covered in the bible there is NO organisation spoken of.
In early christian sect formation, people argued about teachings, as written in the NT. On one occasion, older men of several sects met to discuss doctrines, if anything this indicates a devolution of organisation and an evolution of intepretation and freedom. certainly, meeting to discuss opinion on foreskin does not an organisation make!
If you read the letters at the end of the bible, it is clear that everyone was doing there own thing depending where they lived and what they believed. Again no organisation. The dude paul, roamed about judging people for not seeing things his way, but again that does not make an organisation at all. The only reason pauls books were in the bible, despite them being written 30-70 years after jesus died, paul never even meeting jesus....his books were hand picked by the roman catholic church who supported his romanesque view. Now THEY are the first official and organised group in the history of christianity and we all know they smell dodgy And WT would neverk ever, ever admit it. Do most JW's know that Paul settled and initiated the church? Its baloney to me, but historically there is more evidence for that than the existence of jesus for example.
The nearest thing to an organisation, anywhere in the bible is the anointed kings of israel, a system long ago abandoned by the biblical god. It is dangerous to be under the fickle wavering of one man as evident by history and the bible. Hence that was scrapped by the almighty some time ago.
Then there are the priests and pharisees, who....say what you want about them......did EXACTLY as the bible told them to, they were VERY good people by bible standards. But then the new testament comes along and quite clearly demotes the authority of all those hierarchical positions and makes it very clear it is all personal, you and the big G in the sky, the only mediator being the big J. Again.... No organisation.
Now for me the easy answer is "why do i care what you think of the bible, it is all nonsense anyway!" but then I am an evil atheist. However, as you can see,even biblical reasoning does not in any way shape or form say ANYTHING of an organisation.
If i was you, spend 2 weeks, researching the guts out of this issue because it is the one and only defence they have to exist and it is untrue to begin with. Show the elders the greek words, the other bible translations and the JW 'version'. Go right back to the greek and hebrew and prove them wrong. Use biblical dictionaries and guides and show them there was no such thing as ANY organisation. Dont do it without the research. Also dont celebrate early, let them go away and come back to you.... Empty handed!