Enable the RINs under Settings, Program Settings so you can make sure who is a duplicate or not.
In the Family View display the set of parents with the family group you want to keep. Make sure all the children are added to that family group. With a parent highlighted look at their Info box at the top of the side bar. On the Spouses tab you will see all the family groups they have. The 3 dot menu next to a name has the unlink options. Click on children under the “spouse” in the family group you want to remove the links to, then finally unlink the spouses in the family group from each other. That will clean up the duplicate links and extra family groups.
http://wiki.rootsmagic.com/wiki/RootsMagic_8:Unlinking_People