Who may sponsor or bring the family member, and what immigration/citizenship status must that person hold?
For a dependent child, the person on whom the child depends must be a parent or legal guardian who is a non-resident worker; a dependent child is an unmarried child under 18, including a child physically and mentally incapable of supporting himself. The official source does not state the sponsor's status for a spouse.
See recorded sources
Limits of the record- For the spouse case, G-1 says 'legal spouse'; the sponsor's status is not stated in G-1 itself (the 'dependent spouse' definition, cited in R3, refers to a non-resident worker).