Persons shall be eligible to enter into a civil union only if both such persons are:
(1) At least eighteen (18) years of age;
(2) Of the same sex;
(3) Not a party to another civil union or a spouse in a marriage with any other person;
(4) Not in a family relationship within the degrees stated in Rhode Island general laws § 15-1-1 or § 15-1-2; and
(5) Neither person is mentally incompetent at the time of the civil union.