Excessive growth on leather upholstery... How to proceed?

The warm and moist weather has been enabling these colorful colonities to take over the interiors of our stationary car... Somehow these fungi have managed to get into ALL OF LEATHER UPHOLSTERY, honestly I have never in my life seen nor smelled anything like it.

I'm quite familiar with mold, and how disgusting it is. Is the interior salvageable? How would one even start the process of clean up..? I'd toss the whole car into the ocean. OR hire professionals to clean up and change all of the upholstery. After some professional forensic level disinfecting, bleaching and poisoning. But that's probably expensive.

Just thinking about the smell makes my lungs hurt.

All and any DIY tips, instructions, to-do's and not-to-do's are welcome. Also, equipment needed??

Many TIA!