The Michigan Probate Code is based off of the UPC. Its doesnt require any specific relationship between the parties. Just filing a petition if the person is a harm to themselves or others.

Under MCL Section 330.1434 Petition; filing; contents; clinical certificates.
Sec. 434.
(1) Any individual 18 years of age or over may file with the court a petition that asserts that an
individual is a person requiring treatment as defined in section 401.

(2) The petition shall contain the facts that are the basis for the assertion, the names and
addresses, if known, of any witnesses to the facts, and, if known, the name and address of the
nearest relative or guardian, or, if none, a friend, if known, of the individual.
(3) The petition shall be accompanied by the clinical certificate of a physician or a licensed
psychologist, unless after reasonable effort the petitioner could not secure an examination. If a
clinical certificate does not accompany the petition, an affidavit setting forth the reasons an
examination could not be secured shall also be filed. The petition may also be accompanied by
a second clinical certificate. If 2 clinical certificates accompany the petition, at least 1 clinical
certificate shall have been executed by a psychiatrist.
(4) Except as otherwise provided in section 455, a clinical certificate that accompanies a petition
shall have been executed within 72 hours before the filing of the petition, and after personal
examination of the individual.