In Page View, the Layout Regions of the Multi Layout Regions will be visible only one at a time. Therefore, you must edit them one by one.
By default, when you create a MultiLayout Region, NetObjects Fusion 12 adds a Layout Region.
To add Layout Regions to the Multi Layout Region:
Select the Multi Layout Region.
The Multi Layout Regions Properties Panel appears.
Click the "+" button on the Multi Layout section.
A new Layout Region will be displayed within the Multi Layout Region. The name of each Layout Region is by default LayoutRegion#.