Advise - Office conflicts

I was part of the hiring process in my organization for the team I am part off. For at least a year the newly hired resources got a long like brothers and sisters. After awhile, I distanced myself to the team for my own reasons. When one of the hired employees left, he ended up telling me all the issues going on with the team. I was completely thrown off, and was also told, two of the people we hired are a couple even before joining the company. She even interviewed the partner - which was a huge integrity issue as she should have opted out of the interview for knowing the person. Also found out no one gets along with this couple... however they do work well. Most of us felt betrayed by these people, and they are known to be negative and always complaining about people around them. They always have been the know-it all and walk around like Kings and Queens of the floor. What to do in this kind of situation? They obviously affect the environment of the people around them at work.