I tried this with FTM 2012.
Using a test file I deleted the parents of 5 children. The relationship calculator and chart showed that the children were still siblings. If you create dummy parents to establish the sibling relationship and then delete the dummy parents the sibling relationship remains. The Kinship report shows the brother and sister relationships.
The Family view in FTM 2012 normally has the pedigree view at the top and a family view at the bottom which is similar to your “family group view” If you look in the center of the screen just under the pedigree chart you will see a series of dots. Put your cursor over these dots and you can move the dividing line between the pedigree view and the family view up or down. You can completely remove the pedigree chart if that is your desire.