Looks like i've joined the party late. Much of the issues have been covered, but that said i will add my bit.
The date 607 BCE for the destruction of Jerusalem by the Babylonians is arrived at from within Scripture itself.
There are no dates in the bible, so where he gets this statement from i do not know. All of bible chronology has to have a starting point with secular chronology.
That the exiled Jews would spend 70 years in Babylon was prophesied in many places – 2 Chronicles 36:21; Jeremiah 25:11; Jeremiah 29:10; Daniel 9:2.
The Jewish 70 year exile is only one interpretation of those scriptures. Others being Babylonian dominance of the area, starting from 609BCE at the capture of Assyria to 539BCE. So that all the nations would serve Babylon. Notice Jeremiah 25:11 says 'these nations', not 'this nation'. Other interpretations are a 70 year period from the accepted date of 587/6 BCE for the fall of Jerusalem until 516BCE for the rebuilding of the temple.
539 BCE is a pivotal date – both Scriptural chronology and secular history point to 539 BCE as the date for the fall of Babylon.
In scripture there are no dates mentioned, so your brother i wrong to ascert that the date is scriptural. Secular chronology does point to the date of 539 BCE being correct. This is the pivotal date, the WTS relies on secular evidence here, nothing else.
Scripture then shows that the Jews returned to Judea in 537 BCE.
B*lls*it !! Ask him where. 537BCE is a guess. This is their weakest link in my view, 537BCE is THE pivotal date for this prophecy. They guess it took 18 months for Cyrus to announce his decree after 539 BCE. Interestingly they used to think it was 536BCE, until they realised that Russell had his maths wrong in counting a year zero in his calculations. When Rutherford decided to correct this and place one year from 1BCE-1AD, instead of counting a year forward to 1915AD, which was not an option, they added the year onto 536BCE, so hey presto 537BCE was the date Cyrus announced his decree.
We give primacy to the scriptures that the exile was 70 years, thus the destruction of Jerusalem must have been in 607 BCE.
They interprate the 70 year period as a Jewish exile from 537BCE, the made up date, to 607BCE.
So, when deciding when we think Jerusalem was destroyed, we can either accept the Scriptural chronology (with 1914 following from this evidenced by dramatic and irrevocable change in the world situation i.e. “the last days”)
As shown this is not scriptural chronology....and remember the change in the world situation was not the original prediction. The prediction was Armaggedon would occur.
or go with uncertain secular sources of evidence which are often subject to change, revision and new archaeological discoveries.
Those same uncertain secular sources that the WTS uses to pinpoint 539BCE as the pivotal date. Ptolemy's Canon for instance for which pinpoints 539BCE as the date for Babylon being conquered that the WTS likes to quote from, remember the picture in the Live Forever book? Yet Ptolemy's Canon also pinpoints 587/6BCE as the date for Jerusalem's destruction, suddenly it becomes "uncertain".
The Scriptures will never change that the exile would be 70 years and everyone agrees with 539 BCE for the fall of Babylon, and 537 BCE as the date of the return from exile.
Who's everyone? Everyone who's a JW maybe pinpoint 537BCE as the date, nobody else.
It's good that your brother is talking to you about this and trying to establish a defence. My advice would be not to give him a full response, but just to ask how he arrives from scripture that 537BCE is the date Cyrus announced his decree. The onus is on them to prove their doctrine first, rather than on anyone else to disprove it.
It falls apart at all levels, let alone how they then go on to interprate the end of the gentile times of Matthew 24 with Daniel adding 2520 years and all that.
It's all mishmash.
Paul