Why were the two seamen

DeVriess was a trusted Captain who had helmed the ship through over year and a half of combat operations, and before that (according to the book) he had been the ship's Executive Officer. In fact, when Willie first comes aboard, DeVriess mentions that he's been on the Caine for five years. So, he was well known, liked and trusted by the crew.

I rather doubt Queeg was that infamous. He wasn't that high-ranking an officer to really develop a reputation away from the actual ship he was serving on. In the book, it's said that the Caine was his first command. It was also suggested that Queeg was far better in a subordinate position since he knew that the ultimate responsibility wasn't upon him.

As for the Murphy's Law of War, I don't think it was just an attitude of DeVriess that had the ship looking slovenly, yet performing admirably. In the book, the Caine is clearly a very old ship. It's described has being a World War I era "four-piper" destroyer converted for minesweeping. Most of its machinery is highly outdated and needs fairly intensive work to stay operational. It's suggested that the time and labour required to keep the ship engines and operational systems (guns, minesweeping gear, etc.) functioning properly, combined with having been in the combat area (and thus having been in battle, done combat escort duty, been under air raids, etc), simply did not give them the luxury of keeping the ship in as smart a condition as the DeVriess would probably have liked.

Even after Queeg takes over, the consensus is that there's only so much that can be done to improve the ship. Maryk, who wants to carry out Queeg's orders as a good Executive Officer, but realizes that it's simply not feasible if the ship is to be kept running. Here's how the book describes it:

"He was aware that it was his responsibility to enfore the captain's rules; he was also aware that most the rules were either impossible of enforcement on the overworked, overcrowded, rough-minded crew, or enforceable only at an unacceptable cost to the ship's narrow margin of seaworthiness."

So, DeVriess probably also realized that on ship like the Caine there was only so much he could about spit and polish, and still keep it functioning at sea and -more importantly- in combat. I'm sure that on his next ship, DeVriess would return to more spit and polish standards.