Hello, I'm currently in the process of converting an object, and there are multiple texture maps such as Emissive, Specular, Diffuse, and Opacity. However, I'm not quite sure how to add all these texture maps to the mesh in SimPe. Is there a way to do this?

Depends on the object, and on the textures you've got to work with. The "Diffuse" map is usually the one with the main texture. The others are various effects to enhance/edit the other, but some of them don't work as-is for TS2. It's a bit difficult to tell without looking at the file + textures.

You can look into the shader edit here - it allows for extra texture maps to be used for some of the material parameters.
https://crispsandkerosene.tumblr.co...-for-the-sims-2

It's possible you'll have to edit the textures to work for TS2, though. There's often a difference between what a 3D program uses and what a game uses.

In a lot of cases, the other maps can to some degree be applied to the "Diffuse" map in a texture editing program (by overlays and such), and then you use that one texture for the object. That's often what I do, especially if the "Diffuse" map lacks some details.