Ohh man that is nasty. The carpet can probably be steam cleaned and thus disinfected. My LGT was smoked in, my detailer used a "Neutralizer" in the steam/shampoo solution that made a huge difference.
I would say getting new seats would be easiest if you have the means, way less of a headache then working on them forever and having them still smell.
If all else fails a trio of Squash air fresheners paired with Baking soda may mask it