USUALLY this is not a problem. Please mention that your group would like to be together and we will do our very best to make it happen. Please note, however, that there are never 100% guarantees in either life or campgrounds.
On a separate note, please be aware (respectful) of the added noise/ disruption levels that several sites getting together can create for your neighbors. Large groups with no previous history may be subject to a larger than usual deposit and/or other conditions.