Mold can be really insidious (as well as a health hazard). The best way to eliminate it altogether would be to either replace the cushioning within the upholstery or have the cushioning and carpeting treated with some sort of biocide that will kill the mold (which has a smell of its own).
In a worst case scenario, you can try to replace the seating components with those from a similar non-flood salvage vehicle while still coming-out well ahead.
Depending on how recently the vehicle was flood damaged, however, evidence of mode will usually make itself apparent (one way or another) within 3-6 months. If it's beyond that, you can concentrate on repairing or replacing the wiring and vehicle computer systems.
Best of luck, I hope this helps.