First grow help - dead leaves

Hey everyone, this is my first grow and I want to make sure my plants are healthy. On the 2 big plants the bottom leaves are yellowing and falling off. I hear this is because of a lack of nitrogen, but i used miracle grow soil with slow release ferts so i dont think that would be the problem. Plus the leaves are browning at the tips on my bigger and branchier plant. They havent been watered for seven days because i went on vacation, maybe thats the problem? Plus the plant in the brown container is gimp. It snapped in half but repaired itself, is there any way to boost its growth? Ive used superthrive on the plants.

from my noob expertise .... looks like A .... the need some liquids .... and B - its normal for the lowest leaves to fall off .... correct me if im wrong tho ... cause my two lowest leaves are brown on my 2 plants ... and im not worried