Both parents must consent in writing. In fact, when the couple goes to the clerk's office to apply for the license (which must be done in person), whichever of them are minors must bring both parents with them.
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I agree with both prior posts. Both parents for the bride and groom must consent. You'll need to make a trip to the courthouse with the couple to obtain the marriage license.
Legal disclaimer: Ms. Braaten's answer to your question does not establish an attorney client relationship, but rather is meant to share knowledge with the general public. For specific advise on your case, you need to consult one on one with an family law attorney.