Noel's succulents

I am in charge on Noel's amazing succulent collection while he is away, and posting these pics for him incase he is missing them.

 I am a little bit worried about the plants in the barn, one has a yellow leaf. NOt sure if I should water them.

 I have watered the smaller euphorbia several times and the bigger once once or twice.

Also worried about reddish one front right of rear tray below, gone a bit red.

 Also the smaller cacti twice i think, there hasn't been much sun.

 Is the one below supposed to be this yellow