There isn't a right or wrong answer for how many days. There are so many factors that go into deciding how many days to spend at
Disneyland, for example; how much is this going to cost, when will we be back, love thrill rides or hate thrill rides, love entertainment or hate the entertainment, like people watching, would rather run from ride to ride instead of looking at all the little details, snack and go or sit down and enjoy your meal, etc the list is a mile long on factors. We like going for as many days as we can so we do not feel rushed. Usually it is for a minimum of 5 days. Perhaps you can go with your family for 2-3 days, and then 2-3 days with just your immediate family. I would suggest everyone list one or two things they want to ride, watch, see, eat, etc and plan your days with those in mind. Hopefully you can do ONE item from each person in your family's list. If you don't you may hear a lot of "I don't know where to go" and "I don't care what we do", followed by "I don't want to right that, but that's fine"...... If you make a list, you will have a start on planning for your NEXT trip to Disneyland (with just your immediate family). Going with a group of people, especially with that age range will be challenging, to say the least, and that doesn't even factor in the crowds and weather. Make sure you have plenty of water, sunblock and chapstick with at least sp15 factor. Hopefully the train will be up and running when you go. That will help move some of the crowds.
Check out some of the July trip reports to get an idea of what it will be like. Look at the locations of the rides, attractions, places that have shade, etc so you can suggest places when your group is at a stand still. Check out the entertainment listed so you can get a treat (Mickey's kitchen sink for example) and watch the 5 and Dimers perform in DCA, or grab a Pear-O-Dice drink with popcorn and watch the lights turn on in Carsland.
The Jazz band currently playing on the Mark Twain is fantastic! Great to grab your lunch and grab a table in the shade to enjoy the music and the view. (This is while the river rides and train are closed ). For me, there isn't enough time to "do" Disneyland let alone DCA.