When you reach a point in the game where you can pick the Knights you are taking with you from the Round Table before a mission, choose the person whose item you wish to duplicate and the person you wish to have the item for. The person that has the item equipped must then go into battle and be killed, allowing you to equip the item(s) they had on another Knight. After that, complete the mission and allow the game to auto-save. At the start of the next mission, choose the same people as before. You will notice the Knight you allowed to die has the same equipment they had on at the start of the mission, and the Knight you gave their items has the item as well. This will allow you to have duplicated items as long as you do not remove the item from one of the Knight's inventory. This can also be a good way to save money in the Treasury section of the game, when some of the better equipment is a bit on the expensive side
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 las!
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.