In the account of the treatment of peasants on the farm captured by foreign soldiers during the Thirty Years' War, as recounted in the novel, what is revealed about the perspectives of the peasants?

From what I can see, you would like an account of the capture and ransacking of Simplicissimus's family farm in chapter 4 of book 1.
In this chapter, Simplicissimus relates that the first thing the soldiers did (upon capturing the farm) was to stable their horses. Then, some began butchering (presumably) farm animals, boiling water, and roasting meat, as if they were preparing for a banquet. Meanwhile, others immediately fell to works of "ruin and destruction."
The soldiers ransacked the farmhouse from top to bottom. Some tied together bundles of cloth, apparel, and household goods to carry away, as if they were going to have a large sale. Others shook the stuffing out of the beds and replaced them with slabs of ham, bacon, and other dried meat, as if this made the beds more comfortable to sleep on.
The soldiers destroyed what they could not carry away. They burned beds, tables, chairs, and benches. Kitchenware, stoves, and windows were demolished. Others ran their swords through the hay and straw, cutting it up. Meanwhile, other soldiers flattened copper goods and tinware so that they could easily carry these away. 
Simplicissimus relates that the women of the house (including the maids) were raped and the men tortured mercilessly. He tells of one torture called the "Swedish draught." Accordingly, the soldiers laid one of the peasants on the ground, thrust a gag into his mouth, and poured foul-smelling liquid down his throat. During the Thirty Years' War, the "draught" was said to contain excrement, urine, or even manure. The soldiers tortured the peasant until he agreed to reveal where the rest of the household were.
Simplicissimus reveals that this is how his father, mother, and sister Ursula were captured. Meanwhile, other soldiers made thumbscrews out of their pistols in order to torture the peasants. The thumbscrew was a medieval torture instrument, used to crush victims' toes, fingers, or thumbs.
Each of the soldiers devised their own methods of torture to torment their peasant victims. One peasant was burned in the baking oven, while another had his head crushed with a cord and wooden implement. Simplicissimus tells us that his father was luckier than most, perhaps because of his position as the head of the household. The soldiers tied up Simplicissimus' father, set him before a fire, and smeared his feet with damp salt. Then, they let the farm goat lick off the salt, which led to gales of laughter from Simplicissimus's father.
In this way, Simplicissimus's father was led to tell the soldiers about the "secret treasure, which proved far richer in pearls, gold, and trinkets than any would have looked for among peasants." 
As for the women of the household, Simplicissimus relates that all were raped, even his mother and sister. He remembers their pitiful screams while the soldiers had their way with them. Simplicissimus later chanced upon the household maid in the stables, and she warned him that none could save him from the plight the adults had already suffered. She advised him to run away. 
The narrator reveals that the peasants were resigned to their fate. From the peasants' perspective, their lives were expendable. They understood that they were of little consequence to the soldiers who mistreated them. These peasants had long accepted that they had little control over their destinies. This is why the maidservant told Simplicissimus to run away: with the farm destroyed and his family soon to die, he would have to fend for himself. Thus, running away would be his only option to retain a measure of control over his life.