Hi Barb,
With the differences in ages of your children, I can see how you want to make everyone happy. Your family should be able to experience many of the attractions together unless there is a height restriction or someone is not keen on a spooky or fast ride. This is why I love Disney because most rides a family can experience together.
However, I can see how your teenagers might want to skip the little rides or head to DisneyQuest while you are at Downtown Disney.
Depending on your budget, you can determine how to be connected. The deluxe resorts give you closer proximity to the parks. This means your teens could jump on the monorail to Epcot while you head to Magic Kingdom if you stay at a monorail resort. Or you could walk to Epcot or Disney's Hollywood Studios if you are at the Boardwalk or Yacht & Beach.
If your teens want to shop while the little ones are in bed, maybe Saratoga Springs or All Star Music work for your family. Here is the link that shows you the
room options for your party size.
I also find texting works well in the park and setting a schedule with meeting places as well helps. Also, there are apps which have maps in them so you can find your designated meeting place as well.
As for reservations, you can call Disney at 407-WDISNEY, book online or work with a travel agent.
Wishing you a magical vacation!
Beth