OK. Beginner mistake #1 (and something we have all done) is buying something you like the looks of, without having any idea how to grow it.
Another beginner (and not so beginner) mistake is thinking that knowledge of growing terrestrial plants means you can automatically grow orchids. While there are some basic parallels, the are some pretty important distinctions that you need to understand.
It is a poor understanding of the first item that leads to the most orchid deaths- using a potting medium that is too dense, or waiting too long to replace it, so it holds so much water that it suffocates the roots, killing them. The myth that "orchids must dry out between waterings" is just a poor way of addressing that.
- Unlike terrestrial plants, orchids do much of their respiratory gas exchange processes through their roots, rather than leaves.
- Orchids are cultural "niche" plants. They are very highly evolved, so have much more specific needs than do the far more flexible plants you may be more comfortable with growing.
The cultural specificity means that, unless chosen well, two plants may not do particularly well if you give them the same cultural parameters.
Zygolum, the man-made hybrid of the genera zygopetalum and zygosepalum, will tend to require cooler temperatures and low- to medium light levels, while the miltonidium, being a miltonia / oncidium cross, may like it warmer and a bit brighter. I think those two are close enough though, that you'll be OK if your growing conditions can meet their needs.