I think I have written about this before, but I want to stress again that you really should consider why you are treading the adoption path ahead of time. Some do successfully build a family, but I have heard enough stories that our experience is not all that unique.
This is especially true with a sibling group, since they will likely come already being a "family" in their own eyes, even if they have been separated from their original mother and father. Just telling them they are now in a "forever family" will not change the "truth" imprinted on their hearts and minds that their "real family" is not the one they are in now.
If this can't be changed, as I suspect, it will guide the rest of their lives, no matter what you do.
Keep this in mind.