They will guarantee them as much as they can. Which means unless something odd happens you will have them. Keep in mind nothing is truly 100% guaranteed by Disney, not even that you will have a room at the resort for which you made your reservation. Odds are you will get what you need, but it is always smart to have a back up plan, just in case.
This is coming from someone who twice did not get the room type they had booked, and one time did not get the connecting rooms that were requested. So sometimes stuff does happen and you have to make do with what you get. Hopefully you won't have my bad luck with rooms, but just be aware they can only guarantee to a certain extent.