Persons shall be eligible to enter into a civil union only if such persons both are:
(1) Not:
a. A party to a civil union with a different person;
b. A spouse in a marriage that is recognized as a marriage under Chapter 1 of this title; or
c. A party to a substantially similar legal relationship as a civil union such as, but not limited to, a domestic partnership, with a different person;
(2) At least 18 years of age;
(3) Of the same sex; and
(4) Not related to the other proposed party to the civil union, as provided in § 203 of this title.