Note: Gwenevere cannot die or the mission will fail.

Test 1: This one is fairly easy. Keep Gwenevere outside the area where you fight, and tell her to guard the area she is at. Then, take Percival and Arthur into the area and kill the first Lord to claim your first prize.

Test 2: Again, fairly easy. Have Gwenevere attack ranged enemies and have Percival do the same. To finish this task, take Arthur up to the arrow slinging Lord and defeat him for your second prize.

Test 3: This test, by far the hardest. For starters, the fake Gwenevere is the one right next to you when they start attacking each other. After a few hits he will turn to his true form, the Third Lord, and challenge you to a duel. To make it a lot easier, do the same as in the first test and take Gwenevere away from this magically-inclined Lord. The north seems the best direction, as it has stairwells you can put Gwenevere in to keep her out of range of the Lord's attacks. After that, Arthur and Percival should have an easier time attacking, and not worry about Gwenevere's dying. The silhouettes of the Lord will die after a few hits, giving you a better shot at hitting the real one. However, once all but the real one are gone he will bring them back. Keep hacking at him until he is defeated. If for any reason Arthur or Percival are in danger of dying, run them up to where Gwenevere is hiding and wait to heal them. Then, return to finish off the third Lord and claim your last prize.
During the Test 3, an easy way to distinguish the real Lord is simply setting Percival to attack the Strongest. He will automatically go after the real Lord, and not the silhouettes.

Test 4: This test is self-explanatory. Do not pick up the Lord's gold and you should have no problems whatsoever defeating him. If you are up for a challenge however, pick up this greedy Lord's gold and see how mad you really make him.