Hmm,
So ask any of them to show in the Bible, clear evidence of:
1. A governing body that has any function or authority resembling the current GB. To that, have them show you where it says Governing Body in the bible anywhere? (remind them of what JWs say as to why the word Trinity doesn't appear in the bible to catholics)
2. Use the bible to clearly identify the year 1914 as special?
3. Show clear evidence for "overlapping generations".
Wait for crickets.
Of course the entire "religion" is based on those 3 things.