Goering was one of the main authors of the "Hunger Plan" portion of Generalplan Ost, so less brutal conduct of the Eastern war was not to be expected of him. The holocaust per se mightn't have occurred, OTOH losses to deliberately inflicted starvation would have been very severe on Jews as well.
As regards whether Germany could have defeated the USSR, it's interesting how the "lost cause" rationale for Confederate defeat in the US Civil War gets totally inverted in the Nazi-Soviet war. Southern nostalgics tend to employ the lost cause idea to imply defeat resulted in spite of tremendous moral superiority over the Yankees. The German generals likewise turned their ideas about innumerable "asiatic hordes" into a convenient narrative about inevitable defeat.
But Soviet manpower was not limitless. Had they employed the tactics of the Somme or Verdun to WWII they would certainly have been defeated. They won because on balance their pragmatic and untiring employment of the resources at their disposal was more efficient than their enemies, but they also made serious errors. Had it come down to pure economics, Germany should have defeated the USSR though Germany's use of its resources was in reality notably spendthrift.
I don't think infighting after Hitler's death would have seriously weakened Germany. Chronic infighting was one of the few stable and predictable elements of the system of government Hitler had created. Whether it was carried out overtly or covertly was secondary; the Army would not have fallen into open infighting and nor would it have substantially altered state policy.
Any slender prospect of peace with Stalin would have been almost eliminated by the knowledge -- almost universal among the top Army echelons -- that there were numerous giant pits full of corpses around the Western USSR. Stalin had also recovered his balance after the initial shock of Jun 22. He was a seasoned and tough fighter since his youngest days.
The prospect of Hitler's successor not declaring war on the USA is not very significant either. The US was already well involved in the battle of the Atlantic and its principle contribution to the war was economic, a sphere in which it was in an entirely different league from the other participants on a per capita basis let alone in absolute terms.
Neither with Churchill come to terms. Britain's war effort was sustainable and it had the Napoleonic wars for inspiration. In the event that the USSR became crippled, the RAF-Luftwaffe fight would have been tough but the war was very tough on the RAF aircrew in any case. Longer tours and a consequent slight reduction in aggressiveness are imaginable. Not imaginable is German victory in the air (except in the wildest outliers) or an invasion of the UK before around 1948. But by 1948 the challenge of invading Britain would have been the least of Germany's worries.
Certainly imaginable, although improbable barring some very (actually un-)fortunate rolls of the dice for Germany, is that the USSR might become crippled to a degree that would preclude Soviet victory. More imaginable is the Soviet drive towards Germany becoming so costly and prolonged as to amount almost to stalemate.
Assuming either of these outcomes -- either something of a stretch but certainly achievable for Germany -- and US entry into the war even if delayed and unilateral results in a truly ghastly scenario much worse than the war as actually occurred historically. D-Day becomes perhaps a long list of Anzio-style landings (Jodl suspected Anzio was part of a deliberate policy to create beachheads where Naval support and air supremacy would enable attritional fighting on terms very favourable to the Western allies, not an unreasonable assessment). Any main-force invasion would be delayed by perhaps several years.
But in the meantime, the vast air armadas swarming over Europe leave no room for doubt as to the ultimate outcome.
The Nazis would never surrender even under overwhelming atomic attack. The top 1000 were almost perfectly self-serving. Nazism may in fact be best understood as a psychologically precise projection of narcissistic ideas onto the world at large. The true believers were significant only among the lower ranks of the Nazi party. The top ranks would gladly have used every last drop of blood they could spill to preserve their own.
That leaves the only possibility remaining under the assumptions given as civil war in Germany, but the ideological transformation of the German army was very profound also, so there's nothing to suggest it would have achieved a clean coup. The precise succession of events would have been critical, but a failure like the historic 1944 coup attempt would have strengthened the existing leadership whatever that was. Various other scenarios are imaginable, from 50-50 civil war to a clean coup victory.
Whatever happened, by the time the Western allies reached Berlin the level of bitterness would have been dramatically greater than was the case historically. The consequences are hard to guess at. Churchill was no milksop but he was pragmatic. Truman and Roosevelt OTOH are harder to read.
The postwar world would be dramatically altered either way.