Each model has its own PBR texture that includes a color, specular, roughness and normal map. The maps are JPEG images for optimization. 

Yes. Each building has a vertex group assigned to it for the windows and glass parts of the mesh. In Edit Mode, go to the data properties and find the vertex group labeled "Glass." Click "select" to select all glass portions of the house. You can then assign your own glass shader to those portions of the mesh. 

Yes. You can use them for any purpose you wish as long as you do not sell or redistribute the models themselves. 

To be honest, I don't operate in game engines. The models have non-overlapping UVs and baked PBR textures so they should be good to go. They are relatively low-poly.