Ibuprofen and other NSAIDS rarely affect the liver. Unlike acetaminophen (Tylenol) most NSAIDs are absorbed completely and have negligible first-pass hepatic (liver) metabolism. In other words, the way NSAIDS are metabolized makes liver toxicity (hepatotoxicity) very rare.
You are right about the dosing though. You can take both at one time if it's really needed but it's best to alternate between the two every 3 hours. So take Tylenol then wait 3 hours and take ibuprofen then wait 3 more hours and take Tylenol so forth and so on.