Remember once you tell one person of the engagement news tends to travel pretty fast. It might seem easier to tell a couple of people and let them tell other family members or friends, but this really is not for your benefit as people may feel hurt or angry. A good way to that you are the one telling those most important to you is by have a family dinner. It may be necessary to hold two or three small get togethers to tell everyone the news.
The dinners or get together should be within one week of the engagement. Since you are trying to ensure no one finds out before this event make sure not to tell anyone beforehand. For this reason you will want to schedule these dinners as close to the engagement date as possible.
If the two families have not met yet or are not on good terms the dinners should be separate. If they have not met you should try to have a get together for the two families soon afterwards, at least one with the two of you and the parents. You may also have separate meals planned with close friends.
If either the bride or the groom has children, the absolutely must be told first.
Also, if there are any children from previous relationships they should be told first. You should let them talk about how they feel about the situation, and let them openly express themselves. The children should be told as soon as the engagement occurs. They should be told immediately after the acceptance and given a little time to adjust before the dinner party. Also let them know that you do not want them to tell anyone until after the immediate family is told at the party. If the child or children are on good terms with the individual who is about to become their step parent you may even want to allow them to announce it at dinner so they feel involved.