Rip the drain trays off those pots and add more holes. That type of pot is notorious for draining crappily. The bottom layer of soil tends to sit wet, and you end up with root rot. That plant looks dead of rot form overwatering.
Also, if you added peat moss, you should also have added some lime. You will want to check your soil runoff pH pronto,l wiht a meter or liquid drops rather than a soil probe, and make sure it's okay.
Those pictures are too dark to tell anything useful- they are backlit, they should be brighter- but I almost think I see problems with a couple of the others.