Hi sorry to hear about your uncles distress. The easiest way to prevent kidney stones is also the most effective, drink lots of water. Limit your intake of processed salts and sugar. Drink water or fresh juices with honey instead of soda. Caffine is also linked to kidney stones so try to limit your caffine intake too.
also avoid higher intake of salts and calcium. Recent studies attach more the higher intake of proteins to the higher risk of stones. So keep a tab on it, especially if u have family history. never forget adequate fluid intake.