The only advice i can give right now is this
Small plant + big pot= easily overwatered.
The plants at this stage should be covered with a humidity dome. And only spritzed with ph water for now. When you do start to water the pot, take and only water with 1 liter and only water a circle around the plant. Only water to the circumference of the widest set of leaves. You shouldnt really water for a week or so
PH meter…not phone meter on order. On the soil am very embarrassed to say miracle grow…standing by for the slaps on back of my head. Starting to see the downward curl on the second of three plants. I did notice my room temp was peaking above 87. I have watered and added ventalation have the room down to 78 now. Trying to get it lower.
Getting the temps down to 78 and the light up is a good start. What is the specific type of miracle gro soil you are using? Also can you send new pics under natural light so we can get an up close look at the leaves colors?