What is the ruling on naming a girl "Ma'azin" and what is the criterion for naming children, and what is the ruling on names such as: Al-Sadiq, Mu'min, Al-Salih?

Prohibited names are those that involve servitude to anyone other than Allah, or are exclusive to Allah, or have a blameworthy meaning, or are meaningless, or involve self-praise. The name "Ma'athin" does not fall under this prohibition, so there is no harm in naming with it, even though it is preferable to name with the names of the women of the Salaf. As for naming with names like "Al-Sadiq" (The Truthful) and "Al-Mu'min" (The Believer), these involve self-praise and are therefore prohibited.