The one plant that's really yellow looks like the leaves are drooping down a bit it is a sign of over watering. The root system is still very small for the size of the pot. More than likely the lower and middle of the pot is still wet when the top starts to dry out. If you lift the pot you can get an idea of how heavy or light it is to help give you an idea when to water. Let them dry out a bit more than usual then stick your finger into the soil up to your first knuckle to see if it is dry. Using both of these ways to gauge when to water. If the soil is too wet the roots can't pull in nutrients properly. Everyone is guilty of over watering at some point or another.
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