I also agree that buying one of the better guidebooks (agree also that Birnbaum will be best for your group), do study and make a plan. Understand up front that with four parks and lots of other activities, you are not going to be able to "do it all", so relax a bit and don't try.
Possibly have each member of your group pick one thing they want to do at a given park. As you will be there 12 days, you will have more than one day in each park so you can spread it out. Maybe make one visit daughter 3 and niece day, another visit for your other daughters.
Hopefully you can be early risers, because I am a big advocate of being at your park of choice before opening. It will be coolest, and with evening EMH, more people will be out late and sleep in. You will have a window of about three hours where you can get a lot done before the park starts getting crowded. Then maybe mid afternoon you can go back to the hotel for a swim or a nap.
Especially with a group your size, you need to make reservations for any sit down meal you want. You can check out all the restaurants and sample menues here:
http://www.wdwmagic.com/dining.htm
http://allears.net/din/dining.htm
As others have said, remind the staff at check-in, when you are making reservations, and when you arrive at the restaurant that it is your anniversary. It doesn't even have to be your anniversary "day" it is an anniversary trip, so perfectly acceptable to celebrate the entire time. Do pick up free anniversary buttons at guest services in the park (if they don't have them for you at check-in)
There are many good restaurants, some totally unique to Disney that are great fun for the whole family. 50's Prime Time and Sci-Fi Drive in at Studios, O'hana at Polynesian, Cinderellas Royal Table, Whispering Canyon at WL, Boma at AKL. I strongly suggest doing Hoop De Do Review with the whole group for a casual anniversary dinner (it is family style dinner and a show at Ft. Wilderness). Doesn't sound like you and your wife are planning any adult only meals, so I'll leave that for another time.
Three more things....with all the ladies you are travelling with, there are various character meals and specifically princess meals for you to consider.
Second, familiarize yourself with Fast Pass (FP) it is a great way for you all to get on the more popular rides without a long wait. Just have mom or dad collect all the park tickets (after you have all entered the park of choice) and go to the ride of choice and get these tickets for all. You can get additional tickets after two hours. The guidebooks let you know what rides have FP, and we can also help in identifying which you should look for.
Finally, there is a "tour" held in the Magic Kingdom called the Family Magic Tour. It would be fun with the possible exception of your 14 yo.
Look forward to hearing how your plans shape up. Ask more questions, (hopefully a little more specific :lol
and feel free to PM me as well.
