Magnesium helps a -huge- deal when suffering kidney stones, and is a necessity to lower the symptoms of detox.
My preferred is magnesium chloride (aka magnesium oil) spritzed on the skin.
Having activated charcoal available to use will also help lighten the detox issues (am a regular user myself), and it gives a gentle source of trace potassium. (It must be taken separate from medicines or supplements by 1 hour, with just water. It is an absorber. )
Have you had your brother's vitamin D3 blood levels checked? Low D3 status is -very- often associated with kidney problems. It is an essential nutrient to help carry minerals around in the body.. and alkaline minerals help protect the kidneys while filtering the blood.
If the D3 status is low, use supplemental Ubiquinol (aka coenzymated CoQ10), 100mg/day together with a D3 supplement, and make sure to have some magnesium available to him!
Ubiquinol is another building block for smooth muscle tissue, vital in the heart, liver, kidneys, etc. If it's low, then there'll be a very hard time upping vitamin D3 blood levels.