OR send your mom an anonymous letter (to your father as well) telling them you are a secret admirer of theirs and you want to have a date to do a sex. Surely the comedic hijinxes and the relieving moment they realize they encountered each other , and by logic, the sexing that will eventually happen, will make them a happier couple.
Now seriously, if you have any older brothers or sisters, they will tell you , as did mine, that some couples go through their bad seasons, but they eventually go away. All you SHOULD do , imho, is sometimes stop them if it gets too intense, and try to become a mediator in their fights WITHOUT TAKING SIDES(this helps a whole lot and they appreciate it) Good luck