I am not an expert and surely when it comes to something such as cancer I can only give what advice I can. First off, when he takes the silver is he taking any kind of probiotics? Taking large amounts of silver can kill off stomach flora which could be part of the reason for getting sick.
I'm not sure about any healing crisis, I wouldn't think silver would cause you to go through any phase, except get better.
I would also try olive leaf extract, and mushroom extracts along with pressed fermented wheat germ, mushroom extracts can energize the immune system and the pressed fermented wheat germ may unmask the cancer from being recognized by the bodies immune system.
Along with graviola and Paw paw, may all aid in fighting the cancer along with the silver.
Another thing is nebulizing the silver may aid in fighting the lung cancer.
Umckaloabo is good at fighting viruses and lung infections but can make you nauseous, at larger dosages.
This is just some of the things I found in my searches and experience, what advice I can give if you were going to fight cancer naturally without chemo or surgery.