A couple of years ago we did a big trip. We had 2 adult children and their 5 kids ages 5 and under + my brother and his wife in a BWV 2 story grand villa. It was pretty chaotic with so many young kids. It might work fine for you but it was hard getting these kids to take any naps. If I had it to do over again I would have split the families with young kids into their own rooms and put more adults in the GV. But we had more rooms to work with (the GV + a 2 bedroom + 2 one bedroom units) to house 7 kids and 14 adults. Only you know how the kids will deal with the stimulation of other kids 24/7.
I agree that you would have to be wildly lucky to get a BWV GV if you don't own at BWV.
P.S. Maybe you will have another kid in the mix by then?! That happened to us on one of our big family trips. 11 month booking is longer than 9 month babies...