Ghee, of it doesn't need to be raw, raw heavy cream, egg yolk, warmed sustainable palm oil, macadamia oil, walnut oil, avocado oil, fermented cod liver oil, any form.of suet that you can add to a blender
Id do a combination of raw butter, raw cream, raw yolk, and raw beef liver and blend the hell out of it.
Don't go crazy with bone broth as it has more protein than we think (knocks out of ketosis) and an amino acid whose name I can't recall that tends to spike blood sugar levels, even if macros are correct (loads of people have reported this and it has been clinically studied), which furthers the issue of being knocked out of ketosis.
Hmm I wonder if MCT oil or the bullet proof brand brain octaine would be helpful.
If you want him to get into ketosis as quickly as possible, feed him just fats for three days, then add back in a bit of protein and minimal carbs. I mean, really, he doesn't need any carbs. Most carbs for folks in ketosis are either treats, like chocolate of the occasional berries or something, or sugars in veggies or milk.
I'd recommend a fat fast (three days just fats) and then the other macros in appropriate ratios.
Good luck. I hate cancer. I will post back In here if I can think of anything else.