I would suggest telling them. If you wait too long they will feel that it was due to them. I would let them know that you are pregnant and maybe tell them in a special way. Even though it is difficult for them, they would still want to be included in your good news. I've had many friends in this situation. All of them have found telling is the best way. After telling everyone, when everyone is together, I would just try to find a way to try and keep too much focus off of the pregnancy until they feel comfortable.
Hope that helps. ps. the longer you wait, the more chance they will find out from someone else and then feel insulted that neither of you felt you could tell them.