so it wasn’t all as bad as I thought. The Canon service centre technicians told me that the two camera bodies are fine, no mould or even dust on the sensors. However the lenses are a different story.
The 40mm f/2.8 STM is fine, but there are some spots on the front element, probably from a botched cleaning job and rubbing off of the coating. The 28-105mm is unfortunately too badly infested that the lens is etched, AND it’s such an old lens that Canon doesn’t make spare parts for it anymore, so that’s a goner.
The 50mm f/1.8 is probably a straightforward cleaning, wasn’t too bad. The remaining two lenses, they will try to clean them at first and see how they go, and hopefully wouldn’t require any replacements of the lens elements. The 100-400mm L is also out of support from Canon so if the lenses are scratched/etched then they can’t really do anything about it, which is a shame, that is a great lens.