Fortunately, your computer can help (not with Aunt Bea but with the seating arrangements). Try PerfectTablePlan software from Oryx Digital ($35). Input the names, meal preferences, and other key information for your confirmed guests. The software helps a little by recognizing entries you've made before (like "vegetarian") and pre-filling the last names of same-family relations. Then use the chart to assign seating preferences. A heart means two people should be together, a skull and crossbones means two people should be kept apart, and so on.
Next, set up your reception hall by dragging and dropping tables (you choose the shape and size) onto the floor. Finally, use the software's automated seating function to put guests in their places (so to speak) or place them manually. The software really helps you manage RSVP and guest-specific information, print clear charts and lists, and smoothly handle last minute changes. Your seating chart will be a monster task no matter what, but the benefits of the software probably make it well worth the small price.