Wouldn't joining 2 duplexes needlessly duplicate common areas? I would think a large multigenerational family might want a large family room rather than 2 smal

Wouldn't joining 2 duplexes needlessly duplicate common areas? I would think a large multigenerational family might want a large family room rather than 2 small ones. Likewise the kitchens. They'd have 2 kitchens, one extraneous and both of them insufficient for the task.