This tool handles capacity, not relationships. You still know the family dynamics. Use the first pass to reduce the mechanical work, then make the human decisions yourself.
Practical table planning
Make a first-pass seating plan without dragging names around a screen.
Enter households or groups, their size, your table capacity and the number of tables. The tool will keep each group together where it can, then show anything that still needs a human decision.
Wedding seating planner
Use one line per household or group in the form Name | number, for example Smith family | 4.