First, you and your partner need to agree to an appropriate manner in which to address your son's disrespect. After you are clear on that, you need to sit down, the three of you, and discuss boundaries in your home. Your son, who effectively has been raised by your partner, is trying to divide and conquer, using your partner's inappropriate responses to him as the firepower. He knows he is out of bounds, but the yelling gives him a valid platform...and he defocuses from the real issue - his behavior. You feel caught in the middle because he has placed you there by trying to triangulate the situation - pitting you against your partner, your partner against him, and making it seem that you are pitted against him because of "taking sides". Think about this...this is working in his favor because now you are not addressing his behavior, but everyone elses! By communicating with each person and as a family as a whole, you can circumvent this cycle of poor communication and address the real issues at hand. Try to handle the conflict in a calm but firm manner. Don't make threats, but do follow through on what you say. If you tell your son when he is disrespectful to you or your partner, then he will be grounded for 48 hours, then do it. Nothing is worse than inconsistency in parenting. Say what you will do, Do what you say. Your partner must quit yelling...two wrongs don't make a right. Remember who the adults are and use your authority and consistency to handle this situation - it will improve with consistency, and consequences. Best of luck! PS...I also have a partner with children, but got into the game much later....they were 19 and 21!