Justin has type a blood and his wife brittany has type b blood. justin's parents both have type ab blood, and brittany's parents also both have type ab blood. what are the chances that justin and brittany's son theodore has type a blood

Since parent of both Justin and his wife Brittany have blood group ab, this means Justin is homozygous (aa) for blood group a and similarly his his wife Brittany is also homozygous (bb) for blood group b. Therefore, Justin and Brittany's son Theodore will certainly have ab blood group.