marked by balance or equilibrium and readiness for action
"The God of Thunder" is an epithet ("descriptive phrase") for Thor. A part of Denmark's Norse heritage, "Thor" here is Kirsti's name for a kitten. Annemarie finds that funny because the kitten looks like it'd run from thunder. There could also be a symbolic meaning since Thor is seen as the protector of humanity, and the kitten appears in scenes leading up to Peter and Uncle Henrik helping Jews to escape the Nazis.
The God of Thunder sat alertly poised nearby, watching.
"Fear," "dread" ("fearful expectation or anticipation"), and "consternation" ("fear resulting from the awareness of danger") are all synonymous emotions that Annemarie feels because Uncle Henrik had just asked her, "How brave are you?" Usually, that question is followed by something dangerous, and in this case, it is lying to Nazi soldiers (twice), so that the escape plan would work.
She was startled. And dismayed. It was a question she did not want to be asked. When she asked it of herself, she didn’t like her own answer.
Kirsti had gone to bed reluctantly, complaining that she wanted to stay up with the others, that she was grownup enough, that she had never before seen a dead person in a closed-up box, that it wasn’t fair.
(used of behavior or attitude) characteristic of those who treat others with condescension
"Condescension" means "showing arrogance by patronizing those considered inferior" or "a communication that indicates lack of respect"--both fit the action and attitude of the officer (whose higher rank would make more people seem inferior to him), who believes he can barge into a funeral, who is being disrespectful with his hand on the lid, and who is expressing fake sadness for a woman he never knew and suspects does not exist.
He placed one gloved hand on its lid. “Poor Great-aunt Birte,” he said, in a condescending voice.
Annemarie realized that it was the first time that she had heard Peter Neilsen call her mother by her first name; before, it had always been “Mrs. Johansen”; or, in the old days, during the merriment and excitement of his engagement to Lise, it had been, occasionally, “Mama.”
an ungainly posture with arms and legs spread about
The definition is for "sprawling" as a noun, but the example sentence is using the word as a verb. The definition for the verb "sprawl" is "sit or lie with one's limbs spread out" but this is missing the key adjective "ungainly" ("lacking grace in movement"). Mama is embarrassed about tripping, which forced her to sprawl; and she is more embarrassed by its result: "Your proper mama, crawling inch by inch! I probably looked like a drunkard!"
“Can you believe it? I was very nearly here—well, maybe just halfway—when I tripped over a root and went sprawling.”
Mama's ankle is grievously affected by a swelling, and her stricken face could be partly due to physical pain, but it is mostly because of her realization that the fallen packet means that the escape could be doomed.