Impossible to predict with accuracy. We don't have enough information.
While smoking is a major risk factor for a heart attack
, there are several other risk factors, including high blood pressure
, high cholesterol
, and a family history of premature heart attack. These have interplay, and without knowing the rest of each brothers' history, one cannot tell who will have a heart attack first and die.
While smoking is bad, you are at risk for high blood pressure, diabetes, and high cholesterol, just by being overweight
(In fact, if you have never heard of "metabolic syndrome", you might want to search it on the net. Some doctors believe that a waist greater than 40", high blood pressure, and diabetes or prediabetes, in conjunction with high lipids, magnifies or multiplies one's risk of heart attack more than any one of those factors alone.)
And, let me assure you, diabetes is so bad, it is considered equivalent to actually having coronary artery disease, and physicians are instructed to treat a diabetic as though he's already had a heart attack. Excess weight is a major risk factor for diabetes.
Thus, you are not protected from this fate of heart disease
by not smoking. You need to control the weight to prevent high BP
, high cholesterol, and---God forbid---diabetes. Good luck.