Hmmm… Well, I might have over-parsed it into two sections. Your question promoted me to investigate further. I found this nice explanation of the entire construct んだろう (as a spoken, slurred のだろう).
It is stating a before-said as a fact, or speculating that is why it must be so. Trying to apply that here to (家族からすれば天下の永大教授に頼めば安心だと思った)んだろう, it might apply to (entire) thing.
I OFFICIALLY GOT INTO TROUBLE about my time management and spending “too much time on the internet”. Thus, I regret to say…I may be less ON the board during peak time (you guys peak at 8am to 1pm my time zone), because I can’t be on during work hours 9am to 3pm (and I have that morning run). So… Apologies in advance, but I will be reading your analyses in the evenings!