“die, yes, die.” This is the figure of speech polyptoton, which in this case repeats the same word twice but with different aspects: tense, gender, number, etc. Although it could be translated as “surely die,” or something similar, the repetition of “die” catches our attention and brings emphasis to the text. This is the same phrase as God used in Genesis 2:17, except the verb is singular in Genesis because God was speaking directly to Adam, whereas here it is plural.
[For more on the figure of speech polyptoton and the way it is translated, see commentary on Gen. 2:16, “eat, yes, eat.”]
“thinks of ways.” The Hebrew uses a noun and a verb for emphasis, more literally, “thinks thoughts.” Young’s Literal Translation has, “hath devised devices.”