I'm still a novice to the codes, but I've learned a little since I first posted this. As far as the official Disney codes, I think they only come out a month or two in advance. So, you can do like me and order a full-price pkg... then when the codes come out, call and have your reservation changed. Shouldn't be a problem since you're traveling in off-season. But check out mousesavers.com for other codes (and general discount prices such as park tickets, transportation and cheap eats). Now, don't quote me on this, but I think your family members who are part of DVC can use EITHER disney codes or their own discount. they should just call when the codes come out to find out which is cheaper. If that's incorrect, someone post please!! I don't want to give out bad info.
Anyway, from what I can tell, disney goes crazy with the codes during value season, so you can almost definitely count on finding a room discount (no matter where you are staying) sometime in July or August just before your trip. I just changed my ressie using the code and saved $214 on a four-night stay at a moderate resort!!! Good luck!!