I am glad that the kitten is responding to the treatment hopefully Yoshimi will too, and will show improvement in a few days. Something else that might work is Aloe Vera Juice. it has an antibiotic effect and can be worth a try. I will be talking to my pharmacist in a few days and see if he has any suggestions for something topical. The thing to watch out for is topical products that are good for you and I and or other animals can be extremely hazardous to our cats.
I see you're having fun with the nutritional food for the cats in Mexico. Tuna and sardines make a great treat from time to time but be very careful about using it as a meal replacement. Tuna is known to have negative effects on a cat. As far as the coconut oil goes the only experience I've had is for human consumption.
You're talking about using colloidal silver at 500 ppm. I have had no experience with it. All my work has been involved with 5 to 35 ppm. I know about 7or 8 years ago there was a lot of controversy about the higher parts per million when used as a dietary supplement. But if you're satisfied with the research you have done and you think it will do a job then go for it. In the meantime I'll keep my eyes open my ears to the ground for anything that could be of value to you and let you know.