Regarding laundry, look at the clothes your whole family is taking. Don't take a total of 2 red shirts, or you'll have a tiny load of reds. Make sure you can do a full load of darks, lights, etc.
Towels are my biggest challenge on long camping trips. We wash them more frequently when camping, and our trailer doesn't have a lot of room for towels. I need to get over the "normal" place for towels and put extras somewhere that they fit. You'll still use more than normal, though, because they'll get sandy if you hang them up outside, and you'll want to wash them if they fall on the floor in the comfort station. Because we don't have dedicated hooks where each of us can hang our towels in our trailer and know that they're ours, I write our initials on the tags with a Sharpie so that we know which is whose.
For food, make a good list before you go of easy meals you can make. Have some premade and in the freezer. And think about space. For example, you can premake chili completely before you leave and freeze it, but if you leave out the cans of beans and tomatoes, it will take up less space, and adding some cans at your campsite won't take long at all.