Your cattleya amethystoglossa doesn't look too bad. Some roots may be brown but the others look healthy. I would wait for the sphagnum moss to dry a little between waterings. It should be getting fairly bright, filtered light. I think it looks pretty healthy.
Vanda seedlings can be sensitive. I've never used your method but I don't see why it wouldn't work. It's very common to lose a bottom leaf or two when you first get a vanda. The most important thing for the vanda at this point is root growth. Hopefully you'll get some good roots on it so it will be ready to grow strongly in the spring. If the roots seem to be growing I wouldn't worry too much about the yellow leaves right now. Good luck.
as for both plants: flush the roots because you have been fertilisering it too much...its only weekly weakly in summers when it is growing roots and leaves...crystals on the roots might have formed; so you need to flush the roots with running water...and bright shaded sunlight for both plants
I agree. I didn't see that you were fertilizing every 3-5 days. That's too much fertilizer. Weakly, weekly is perfect during the growing season, like Bud said. You can also do that during the winter for the vanda if it's growing. The cattleya probably won't grow much during the winter so it doesn't need much fertilizer. Every two weeks or even once a month could be sufficient.