Click one of the desired models to set it as the dominant model (meaning the model whose fields will appear in the fields area). The dominant model is indicated by a green outline as above. Then,
2.
Shift + click the other desired models. These models are indicated by yellow outlines.
The small NE icon at top left of the multimodel area always indicates repository mode. For any of the other models an NE is in, they will get the role-indicating shape you have set for them in that model. If you have not set a shape for an NE, it will be indicated by an NE icon as well.