Two captains
Unfortunately often pilot performance goes out of the window when two mates fly together...The confusion one can also see with PF and PNF incident reports such as the recent irish one.
My first carrier had a ridiculous proceedure of the non flying pilot handling the throttles which again wasn't optimal in several ways.
It would appear that one "captain" had his head in the cockpit trying to synchronize the engines and I wouldn't be surprised if the other wasn't aware of what he was doing and vice versa.
Mountain flying as per the French gliding description of below the crest (vol de pente) is a complicated science which has no givens.
It envolves flying at times under a wing span from the face depending on the steepness of the slope, at an initial speed with energy in hand and ALWAYS WITH AN ESCAPE PATH.
In extremis one can be surprised as I was on a slope bordering the quarry adjacent to the Cape Gliding Club where I found myself and student inverted at 200ft agl.
The thermic activity generally follows the up slope even in the lee, breaking away from trigger points, converging above the crests and with down drafts away from the slope and often in the middle between two crests. (Except when the airflow has gone katabatic).
Low performance motorised flying machines are a danger as downdrafts can easily exceed 2,000 fpm and that is without any wave or rotor influence.
Neil Williams, a former British aerobatic champion who had the wing fold on a Zlin, died flying a Spanish Heinkel 111 in the 1970s doing something similar but with his wife and a couple of engineers on board.
Similarly it is thought that Steve Fossett, the round the world baloonist who tried to set a new world record height gain, did something similar.
Neither of these had fare paying pax on board nor the same level of oversight from the regulators.