COMPLETE TEXTURE AND FIXED NORMALS (EXPORT FORMAT)

Good Day! I did a quick overview online how to export multiple meshes (6million verts+), I actually did it by category but the results of importing it wasnt good like when doing it on another rendering engine like Lumion it has an automatic texture based on what you have set on your 3D Modelling program but here in Unreal it was incomplete and a lot of missing faces and textures.

Is there any option like force double faces so I dont have to go to modelling mode and fix the normals? Also about the textures was there any export format to be used for a complete texture that I’ve set to?

Thanks, I do really appreciate the help.