Terrible Two's just keep going

We have a three year old living in this house that has never left the terrible two's. He never ceases to amaze me with all of the trouble he can get into. His mother never makes him mind when she is in the house. All she does is yell at him and never accomplishes any sort of discipline with him. She yells at him and he yells at her and we all go to our various rooms and shut the doors and either turn TV on very loud or start listening to our MP3 players. Well today during his nap time which was in my daughter's room because his baby sister was sleeping in their room. He managed to somehow get into the Turkish Delight Candy that my daughter brought back from Holland with her. Now mind you this small bag of candy was over $10.00 U.S. Well we must not have liked the first, second or third piece because they were all stuck in various places on the bag and the bag was not sealed. Then we discovered he had gotten a sharpie marker and marked on the outside of a DVD case. So to say the least he is banned from our rooms. He can sleep in his Mother's room and if he destroys everything she owns then so be it. We have tried to talk to his mother and to help her with him but when we get onto him when she is in the house for something it only makes her mad and she starts in on my daughters children. So we just let him go when she is home. Makes for fun evenings when she is in the house.