WHY DO FORIEGN KEYS HAVE TO BE UNIQUE OR HAVE A CONSTRAINT?

How do I go about protecting rows from deletion in this scenerio?
Rule 1 The Administrator Users Account may not be deleted
Rule 2 All Groups have Administrator as a member, and the Administrator cannot be removed.
Rule 3 All Groups have the Administrators Group as a member, and the Administrators Group cannot be removed.



Four tables:

Users Table (
UID bigint Identity seeded with 1234 Primary key
UserID varchar(30) NOT NULL UNIQUE

)
INSERT FIRST RECORD (this record needs to be protected from deletion)
UID = 1234
UserID='Admininstrator'

INSERT FIRST RECORD (this record and others can be deleted)
UID = 1235
UserID='Test User 1'

Groups Table (
GID bigint Identity seeded with 1234 Primary key
GroupName varchar(30) NOT NULL UNIQUE
)

INSERT FIRST RECORD (this record needs to be protected from deletion)
GID = 1234
UserID='Admininstrators'

INSERT SECOND RECORD (this record and others can be deleted)
GID = 1235
UserID='Test Group 1'

Group_Members Table (
GID bigint NOT NULL //points to the group's ID and can't be unique
UID bigint NOT NULL //points to the members UserID and can't be unique
)
INSERT FIRST RECORD (this record needs to be protected from deletion because UID points to the Administrator)
GID = 1234
UID = 1234

INSERT SECOND RECORD (this record and others can be deleted because UID does not point to the Administrator.)
GID = 1234
UID = 1235


Group_Group_Members Table (
GID bigint NOT NULL //points to the group's ID and can't be unique
GGID bigint NOT NULL //points to the group members GID and can't be unique
)
INSERT FIRST RECORD (this record needs to be protected from deletion because GGID points to the Administrators Group.)
GID = 1234
GGID = 1234

INSERT SECOND RECORD (this record and others can be deleted because GGID does not point to the Administrators Group.)
GID = 1234
GGID = 1235


I have tried using foriegn keys, constraints an every thing else, but I hit a brick wall because FK requires the ke to be primary (btw is UNIQUE).
Any help would be appreciated.