Both Mortifera and Celestia are Noktu projects. Neige just happened to contribute vocals to Mortifera, but otherwise it's Noktu all the way. Noktu also played session bass for Peste Noire which happens to feature Neige on guitars but he also does some vocals alongside main vocalist Famine.
In all actuality, the only projects you can truly say belong to Neige are Alcest and Amesouers, and both of those are only EP releases to date.
(Actually, Alcest previously had a demo out, Tristesse Hivernale, featuring 4 songs, none of which appear on the Le Secret EP).
If you are a true Neige fanboy, you will own a copy of the Alcest demo. Only 300 in existence.