With all due respect, you don't know my parents, and the idea that you know the "solution" for their problem is pretty presumptuous. Some people just aren't compatible. They tried, they stayed married and have, but at bottom they don't like each other --- and seeing as how they're each living with the person who in all the world knows them best, they probably didn't arrive at that conclusion cheaply.
God bless them for sticking together anyway for their children's sake and their own. It says a lot of good about them even if they have such incompatabilities...and I believe in the end, they will realize that they love and cherish each other, even with the problems, more than they realize.