how to import objects from an OBJ file as separate

As you can see in this image, the separate objects (meshes) in an OBJ file get imported as 1 Part.

But I need them as separate Parts to assign different materials to them and be able to do an EMS simulation.

How can I do that?

Second question, it appears the Parts need to be solid and are now considered hollow? How do you change that?

Thank you.