I can imagin how frustrating this could be for you. It can be depressing to see your parents quarrel and fight, especially when this happenns often.
Nevertheless, I would like you to know that it is normal for parents to have disagreements. Most couples do have disagreements. So, it may not be true that your friend’s parents never quarrel. Some parents are able to manage their conflicts without letting their children know about them. Your friend’s parents may fall into this category. However, some parents may sometimes find it difficult to contain their conflicts, and this could be due to stress or pressure. This may be the case with your parents.
You need to find a polite way to let your parents know how unhappy their frequent quarrels and fights make you to be. You do not need to judge between them and you should also avoid taking sides with either of them. You may consider writing if you are too shy or angry to talk to them. You may also start with the parent you are closer to.
Please, remember that your goal is not to criticise their actions or say who is rght or wrong. If possible, do not get involved in the details of their disagreement.Your goal is simply to let them know that you are not happy about their fights and that you would be happy if they can always live in peace. Also remember that your approach should be an appeal to your parents and not a command or an instruction. They are your parents and you must at all times relate with them in a respectful manner.
Most parents would be touched when they realise that their children are being negatively affected by their fights but if your efforts fail, you may need to talk to a close family member whom you know they both respect and would listen to.