No. A competent patient should have the final say as it is his body and he has the sole right to decide. Family members may have their reservations which they can discuss with the patient but they cannot overrule his decision.
I don't believe relative have any role in decision making of any procedure. If patient is mentally competent and the benefits of surgery outweighs the risks for the patient, I would go with the patients decision. If patient is not mentally competent, I would take a medical decision based on what to do in patient's best interest and spend time to explain to relatives (with a witness) my reasons to operate and not to operate and the risk benefit ratio. In my practice I have noticed that some of the relatives making Hugh and cry have not even bothered to see this Gran for years but in the last minutes and hours of their life, they all seek to show that they were in attendance. Get the legal team if necessary (the chances are you will lose as they too are a bunch of idiots), but you have something to document that you had to act again your better judgement.