Von Krockow quotes the "Phaeton has fallen" quip from Heinrich post-Kolin, as well as Heinrich being overheard to say, when celebrating his 30th birthday on 18th January 1756 and hearing about Fritz' treaty with England: "The idiot will plunge us all into misery." (Though as opposed to "Phaeton has fallen", which is a letter quote, the later remark doesn't exist in writing but was reported years later, so take it with the due caution of anecdotes written with the benefit of hindsight. Of course, it's possible Heinrich guessed that by allying himself with Britain at a time wheren England and France were duking it out in the American colonies, Fritz had just given the French the last incentive they needed to respond positively to MT's overtures, but then again, everyone, including him, was surprised by the Diplomatic Revolution. Both he and AW found out about the Fritzian decision to invade Saxony pretty much with the rest of the army, but by then this was no longer a surprise (that he didn't tell them about wars he intended to conduct, that is, despite AW being his heir presumptative).

As for AW, it's worth noting that as opposed to his youthful reaction to Fritz invading Silesia, which was basically "You're the coolest, Big Brother! But why didn't you tell me anything! Can I come, too! Wow, just wow!", he in the 1750s had a far darker view of war in general. In 1753, he wrote to the French Ambassador from Spandau:

"I'm getting up at four and am shooting at sparrows until seven. If one looks at this from a philosophical point of view, it sounds ridiculous, but if one considers that it's practice for the annihilation of human life, one wonders: where in this is our humanity? By now, it has become such a well practiced habit in the world to murder each other that the passing of time allows a crime which can't be justified through anything. The defense of our fatherland, the support of our allies can force us to see this with different eyes. That's why we go through the motions here. Add to this a pinch of vanity, and you are getting the picture."

(The French ambassador in question was that same Marquis de Valori who once quipped about Fritz: "Il n'est guère possible d'avoir plus d'esprit, et il est très possible d' en faire un meilleur usage.")

So basically, the dccumented reactions from both him and Heinrich in 1756 as to what this implied for Prussia can be summed up with "Shit, shit, can't we at least persuade the French to like us again, argh, must join the war effort to save the country!"

Von Krockow also quotes this bitter assessment from Heinrich in 1760 (i.e. at a point where AW is already dead but Heinrich himself, even in Fritz' estimation, has emerged as the major military talent of this war)where he writes to Ferdinand: "You are kind enough to ascribe the saving of the state to me; but even if I had all the abilities you are ascribing to me, they wouldn't be of any use, since I can't go against the will of the one who is dragging us all with him. He who commands under the King loses honor and reputation. (...) 'The State', my dear brother, is a name that gets used to throw sand into the eyes of the public; a villain who claims every success for himself and whom one serves like a human sacrifice."

To be fair, cahn, Fritz famously post Seven Years War toasted Heinrich, in public, as the only general, including himself, who never made any mistakes in said war. How Heinrich reacted to that one is nowhere described. Von Krockow guesses he probably just bowed silently and went home to Rheinsberg.