Looks like approaching the dividing range from the W they diverted to right of planned track until perhaps able to see a gap below cloud and over top of the range, ducked over the range near Pilton, then ducked down one of the valleys running ~NE until resumed track to intercept the northern VFR route through Amberley airspace. Not an unheard-of scenario for a lot of VFR pilots returning to YBAF when the clouds press up against the range, though most go south to Cunningham's Gap or Spicer's Gap. Passed quite a few ALAs near the end e.g. Gatton, Coominya, though. Was the ACFT and pilot IFR rated? If so, and if plan B (ALA or off-ALA landing) wasn't an option, a plan C could have been to turn away from high ground, climb to lowest safe and ask Amberley Approach for assistance as a PAN.
Very sad for the families - lost some good folks by all accounts.