Forget about money being the "root of all evil," instead think of it as the root of all stress. More couples fight over money than sex. As you can guess it is the lack of money that is the cause of the fights. I have never heard of people fighting over having too much money but then again I am not living in that social circle.
Stress is the result of worrying about the lack of money. It forces people to act out wrongly towards others in the form of verbal and physical fights, as well act irrationally such as using payday loans or robbing a bank. So what is the cure? Simple, talk.....talk to each other about the money in the family. Talk about it as if it was a tool or a appliance, don't get emotional about it. Money should not invoke feelings either good or bad. It is a thing not an emotion. Once you have removed the emotion from your "talk" you should come up with some good sound ways to tackle the problem at hand, all without stress.