The time of year that we are going is supposed to be the slow season. However, the time that we leave is the beginning of the busiest time of year at WDW. With only half of the Pop Century resort finished and open, it's got few rooms available than any of the All Stars alone. I don't know how quickly it will fill up. I know that when the announcement was made that it was opening lots of folks on the many many internet boards made reservations to be among the original guests of the hotel. The fact that it is a Value resort makes it appealing to lots of families, obviously.
I guess my best advice from dealing with trying to coordinate extended family vacations on more than one near disasterous occasion would be to take care of you family's needs now. If your other family members can't get their ducks in a row, it's on them. Do what you have to for your own first. You might be surprised just how quickly other people get their minds made up and their butts in gear when they see you have done something with or without them. lol
I think that making reservations anytime within the next month should be pretty safe still. Good luck! Mickey