Will his previous 3 misdemeanor DUIs affect his traveling options overseas especially his chances of getting back into the country?

That entirely depends on what are the misdemeanors. I need more information regarding the crime: 1) What was the exact conviction? 2) When was the conviction? 3) Did he plea guilty or no contest? 4) Did he have an immigration lawyer's advice? 5) What was the sentence of the crime? 6) How much time did he actually serve? 7) Did he have the green card? If so, when and how? 8) Where was the crime? 9) What the court Federal or State?