Cooking two turkeys of about the same weight does not double the roasting time. Cooking time is determined by the weight of one bird. Just make sure there is sufficient oven space for proper heat circulation. All poultry should reach a safe minimum internal temperature of 165 °F as measured with a food thermometer. Check the internal temperature of each bird in the innermost part of the thigh and wing and the thickest part of the breast. For reasons of personal preference, consumers may choose to cook poultry to higher temperatures.
Source: AskUSDA
Learn more tips on roasting turkey as well as thawing frozen turkey, storing leftovers and more.