I do enough shirts for 1 each day (maybe 1 extra if that person if particularly messy/young), and about 3/4 bottoms. So if we're going 5 days, 3 bottoms. If we're going 7 days, 5 bottoms. Etc. We can rewear a pair of jeans at least twice. If the weather is chilly, I'll bring some extra layering options, and a jacket. Then I pack enough underwear and socks for each day, plus 1-2 extra for the kids, just in case of accidents or getting feet wet. If we going to be gone longer than 5 days, I'll bring two sets of pjs, otherwise, just 1 each (unless there's a young child, then I'll bring more, just in case).
Though honestly, if its more than 5 days, I'd probably just pack a mini bag of tide and quarters and do a load of laundry at the hotel if needed, and cut back on clothing.