Jeez, where to begin? It's all human factors, of course.
Get-there-itis is more likely to affect a younger person. Patience, and even a willingness to disappoint people waiting for you, come with age.
The hinky chain-of-command (and possible background personal friction between the two "pilots") meant that it was unclear who was the captain -- the person who was to make the definitive decisions. An airplane or vessel must be a clear dictatorship, however friendly.
Texting while piloting? Really?
I believe that cross-country flying (especially in a high-performance plane), keeping tight schedules and carrying passengers, is not reasonably safe without IFR capacity in both pilot and aircraft. The urge to "press on regardless" is overwhelming. A G.A. airplane isn't a substitute for a car unless it is loaded with electronics and has a pilot who knows how to use them. Even then, it's got only one 1940's-designed piston engine, no in-flight de-icing, and can't fly above the weather.
Sounds like Dad was an Alpha Male ("I got this!") who allowed pride to blind him to the fact that he was getting overloaded and out of his depth. Both young and old Alphas do this; the older ones may, as Abid suggests, may be especially unable to review their current abilities objectively. An older Alpha is apt to get extra-angry if he's not performing well and his "subordinates" are seeing it happen. The anger reduces his performance, making him angrier still, and cycle repeats itself. Anger makes a normal person very, very stupid.
BTW, over the years, I've made just about all these mistakes -- in backpacking, sailing and flying. The fact that I'm here and this Bonanza crew is not is dumb luck. You only can hope that you learn from surviving these near-death experiences.