This interview gives the reading of the family name as みずき instead of みづき, which is honestly better for the kanji anyway:
https://www.4gamer.net/games/442/G044297/20190422072/. I think I took "Niito Miduki" from their blog username but that might not be correct, the "miduki" part of that may have come from their other name 獅子王院みづき
A song they wrote for Nekopara was included in the game MUSYNX and the credit there is to "MIZUKI ARATO," but that seems like a mistake given the above interview