When you say "with barely any true soil" I cringe a bit. Perhaps you picked up a mix which is appropriate for terrestrial Orchids, but not for an epiphyte?
I probably would remove the companion plant while placing the plant into a proper medium. Picture this Orchid growing in nature in leafy compost of sorts in a tree, slightly tilted so the rain water doesn't collect in the crown.
When you talk about yellowing leaves - how yellow? only old leaves turning yellow? How much light does the plant get? Too much?
A picture would help.
