Are his kidneys failing only due to high creatine? Or does he have diabetes, congestive heart failure, or an overuse of NSAIDs?
Uncontrolled high blood pressure, uric acid damage, infection, severe electrolyte imbalance, and medications are a few other problems that can be severe to the kidneys. I think excessive use of protein can affect the kidneys too.
Ginger does improve circulation, which will help to cleanse the bowels and kidneys.
Nettle leaf is one of the best kidney tonics; especially due to the vitamin C and silica, which strengthen the blood vessels and tubules in the kidneys.
Schisandra berry is also very good for the kidneys (and several other things as well).
https://www.herbs2000.com/herbs/herbs_schisandra.htm
And don't forget water. Elderly people do not seem to drink enough water. That will help to flush the kidneys.
Meanwhile, I'm interested to know how creatine and damage the kidneys. I've taken that as a supplement off and on for several years. Mostly off. I take it with CoQ10.