So you are saying that you have a table like this:
CREATE TABLE Groups (GroupID int NOT NULL PRIMARY KEY,
Member1 int NOT NULL,
Member2 int NULL,
...
MemberN int NULL)
That's a very poor design. You should have a table GroupMembers:
CREATE TABLE GroupMembers (GroupID int NOT NULL,
MemberID int NOT NULL,
CONSTRAINT pk_GroupMembers PRIMARY KEY(GroupID, MemberID)
)
This will make your life a lot easier.