What is the ruling regarding the guardianship (Waliyah) of a female slave (Ammah) who has a master (Mawla)?

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If the community (Ummah) has one master appointed for the slave, he is her guardian. If she has two masters, the guardianship belongs to both, and neither may act independently without the permission of the other, as each only possesses half of the guardianship. If the two masters dispute, the Sultan (ruler) cannot act as a substitute for them because the marriage transaction is a disposition of property, unlike the marriage of a free woman where the marriage is her right and benefit. The slave's marriage is the right of her master, and the benefit accrues to him.