How to Load Multiple Families into Revit at once, also known as Batch load.
Multiple families can be loaded into Revit at once using the 'Bulk Load Families' button in the AVAIL Browser for Revit. It will appear when you multi-select families, by holding the Ctrl or Shift key and selecting families. See image for example.
Please note -- you can select as many families as you'd like and load them in all at once, but at this time if you perform a search or select a tag while multi-selecting it will refresh the selections and start over.