Even telling you over the phone, and having it printed on your reservation, does not mean they are really guaranteed. They do pre-assign rooms a few days out. However, your room is not your room until they hand you the keys. The person you talk to on the phone has nothing to do with your room assignment.
Go to Disney's web-site. It states right on it that connecting rooms are a request only, and no room location is guaranteed.
As I've stated before twice now I've been bumped from a paid for room category to a less desirable one. And one time I had even done on-line check in! Maybe the odds of not getting what you want are small, but they are still there. I would hate for any of you who are stating you have to have connecting rooms to show up, only to be told there were none available. I can tell you, not getting what you think you had booked is extremely frustrating.
And, in my experience, they will not upgrade you to fix the problem. The last time I didn't get the preferred room I had paid for I was told that all they could offer me was a standard room. And yes, I did speak to the manager on duty. So don't depend on being bumped up to a family suite. At most they will offer to move you to another value resort that has connecting rooms IF one has them available.
Disney guarantees nothing. Please don't go on your trip with blinders on, thinking they do. The only way to be sure you are all in one space is to book a suite or villa that you fit into. Otherwise there is a small chance you won't get connecting rooms.