David never sought revenge against Saul's family. When two men snuck into Ishbosheth's room, cut off his head and brought it to David, David had them killed for killing an innocent man. (See: [[rc://en/tw/dict/bible/other/avenge]])
When two men brought Ishbosheth's head to David and expected to get a reward for it, David condemned them with the rhetorical question: "should I not now require his blood from your hand, and remove you from the earth?" (See: [[rc://en/ta/man/translate/figs-rquestion]], [[rc://en/tw/dict/bible/kt/condemn]] and [[rc://en/tw/dict/bible/other/reward]])