I imported my low-poly 3D models that I built, posed and textured in blender and exported as FBX files into unity, and I believe I might have done something wrong with the texturing (I am new to this) because the sails of the ship are invisible and non-interactive from the front but visible from the back. It also does this with various other objects from other set pieces, but I'm struggling to find the overlapping problem as they are not based off the same shapes and have different materials. Any solutions, suggestions or advice would be appreciated.

If there are red faces, select them then go to "Mesh/Normals/Flip"

Then you're ready to export you model to Unity.

This practice is the best one, since you're not going to add more faces, nor rendering both faces, what whould duplicate the processing consumption for that model.

I hope I help you!