Hi, Cassandra!
It is of course up to you, but when I am on vacation, I want to be "on vacation" and packing as few lunches as possible! With 6 adults, I would go for the
Disney Dining Plan. Your 4 year old will get charged only a child's price which is very reasonable, and you 1 year old will be free (she can share off an adult plate for no charge, this works best at buffets/family style dining.)
I think that the grandparents would have so much fun seeing your little princesses at the character buffets plus it is a great way to meet many of your Disney Pals without waiting in lines in the parks. I suggest Chef Mickey's, Crystal Palace, and Akershus Royal Banquet Hall.
The menus for children are very healthy and kid-friendly. Even the pickiest of eaters will find something they will enjoy. If you do not see something on the menu, ask your server as they can often accommodate particular appetite!
Of course, another option is to skip the Dining Plan, and do some restaurant dining (just paying out of pocket) and pack some grab and go sandwiches for a few lunches. It is up to you, but for convenience, you might want to give the Dining Plan a shot.
My advice is to take a break from grocery shopping, make some
Advance Dining Reservations and enjoy the great dining around Walt Disney World ! Enjoy!