This double negative emphasizes that a hundred foreskins is the only price that the king desires. The verb for the second phrase may be supplied from the first. Alternate translation: "The king desires only a hundred foreskins as price for the bride" or "The king does not desire any price for the bride; he desires only that you bring to him a hundred foreskins" (See: [[rc://en/ta/man/translate/figs-ellipsis]] and [[rc://en/ta/man/translate/translate-numbers]])
This can be stated in active form. Alternate translation: "to get revenge on the king's enemies" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here "fall" means to die. The phrase "by the hand" is an idiom that tells us the means by which something will happen, in this case, David will be killed by the Philistines. This can be stated in active form. Alternate translation: "to have the Philistines kill David" (See: [[rc://en/ta/man/translate/figs-euphemism]] and [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-activepassive]])