Den spectabile spots on young leaves

[estación seca]

Dendrobium is an enormous genus, with different species from a huge geographic and climate range. If you're going to pot plants together, they need to be from similar climate types and sun exposure.

Dendrobium officinale requires very different conditions from crocatum and usitae, and it is not likely to enjoy growing with them at all. I would suggest removing the officinale and potting it up by itself. Den. officinale needs a cool and moist summer, with temperatures like SF outdoors, and a very cool winter, like SF outdoors, but mostly dry. The other two need to be warm to hot and moist all year.

A good place to read about orchid species is the Internet Orchid Species Photo Encyclopedia.