Please recommend advice for my son 26 who got gall bladder stones and does not want operation to remove it?

That's his business. This is between him and his physician. Don't try to change his mind. You'll only make him angry. If the stones make him miserable enough, he'll change his mind. And many physicians recommend leaving asymptomatic or only moderately annoying stones alone.
Like my colleague... As my colleague describes, your son should speak with his physician / surgeon. Your son's history and exam help determine the risks and benefits of gallbladder removal for gallbladder stones and only your son will have the info and ability to decide. Interestingly, gallbladder stones do not always require gallbladder removal and so determining the risk vs. benefit is key as with all procedures.