🔼The name Malluchi in the Bible
It may also be that Malluchi is not a personal name but rather an adjective, or more precise: an ethnonym to be translated with "the Malluchites". It's true that the other names in the list of Nehemiah 12 aren't adjectives but perhaps the Malluchites were the only household known as such.
Many commentators equate the Malluchi of Nehemiah 12:14 with the Malluch of Nehemiah 12:2, but there's no real need for that.
🔼Etymology of the name Malluchi
The name Malluchi is one of many derived from the noun מלך (melek), meaning king:
The letter י (yod) upon which our name ends, most likely marks this name as an adjective: meaning either simply Malluchites or literally Kingly. But technically spoken, the final yod may also create a possessive form, meaning My King.
For a meaning of the name Malluchi, NOBSE Study Bible Name List reads the same as for Malluch, namely Reigning. Alfred Jones (Dictionary of Old Testament Proper Names) also equates Malluchi with Malluch, which he too translates with Reigning. BDB Theological Dictionary doesn't see the need to propose that Malluch and Malluchi are the same man, but translates neither name yet lists them both under the noun מלך (melek), meaning king.