twin orchids one does well the other loses all its leaves

[madimae]

Hi! My name is Madi, I have kept orchids through university (3yrs now) and am pretty much self taught and very much a beginner. I used to get my orchids by picking them up from shops when they are out of bloom and on sale for cheap. That being said I can keep them alive but never had one bloom until I found a specialized orchid shop that "babysits" and even then my only flowering plant got bud blast and lost all but one bud that isn't holding on so good. So I'm still struggling through understanding how to get the perfect balance.
So the story goes Dad wanted to put orchids on the front step on the wall. I warned him that they aren't meant for outside but they would be out of direct sunlight and brought in at night and we live in a warm climate. So I bought him 2 orchids from my shop I found. They were 2 big plants each with 2 flowering stems and 4 or 5 huge leaves. I believe they are moth orchids. So at first they both did really well they kept blooming and all the buds grew and bloomed but then one of them started losing its leaves. Eventually all the leaves came off and the flowers died. The other orchid, mind, was still blooming away. They lived in the exact same conditions 2 ice cubes every 10 days they came in and out at the same time. So when the plant lost everything we were confused. Dad gave me the "dead" one and I'm trying to save it. I have taken it out cleaned out all the dead roots with a sterilized knife, rinsed the good roots, and repotted it in a fresh bark mix. So my questions are why did it"die" and how can I save it?