Whats the approximate distance for a two day hike?

I've found that most people, such as my wife and children, whether unused to hiking, out of shape, or children can barely be coaxed into hiking 3-4 miles in the High Sierra and perhaps up to 6-7 miles at lower elevations under cooler temperatures with minimal elevation loss or gain, which is my answer to your question. The farthest I've ever hiked in one day, solo, is 21 miles in around 7 hours in the Sierra. I wasn't trying to break any personal record, I just wanted to see a particular area and didn't want to backpack alone.