how to convert ortho 2d photos convert to 3d

That's more of a photogrammetry task and there's no way to do that in FME. (in fact, if I recall my photogrammetry classes from college correctly you need stereo pairs, rather than orthophotos, to be able to generate a 3D model)

I don't really understand what you need to do or what data you have available.

I guess that if you have orthophotos and a DEM or TIN you can drape the protos and create a textured mesh or a colored pointcloud.

Please give us more information on what you are trying to achieve and/or some sample data and an example of the desired finished product.