Alyssa,

Is the entire main root mushy? If not, your 1st experiment: Cut off everything mushy. Dust the entire root area with cinnamon and repot in barely moist 50/50 cactus mix / perlite. Do not water for a week and keep it furthest from your lights. Then begin watering scantly, around the rim until the seedling improves.

About your watering ... Once the seedlings are a month old, they do not need misting. Water once a week to runoff. Do not allow pots to sit in standing water. As a general practice, it is never a good idea to fertilize a dry plant. Don't let fertilizing be your main watering. In my climate, I water one day and fertilize one or two days later.

If you currently water once a week, bottom feed by placing pots on a tray and allowing the seedlings to "drink" their fertilizer from below for a minute or two. Each seedling will only take up what it needs. You can begin feeding as a 2nd weekly watering once the weather warms up.

I hope you are able to save these two seedlings. Adeniums are surprisingly strong and self correct with a little help (or not). Keeping my fingers crossed for you.

Maria Elena