You can load Revit models (*.rvt) into a project as a group, and you can load Revit family files (*.rfa) into the Family Editor as a group.
To load a project or family file as a group
When you select attached details, detail elements in the file are loaded as attached detail groups.
The file is loaded as a group, and the group displays in the Project Browser under the Groups branch. You can now place the group in the project or family. See Placing Groups.
To reload a group
If any family types differ between the file you are loading and the host file, the Duplicate Types dialog opens to indicate this.