I am thinking a southern window is too much sun unless you have a sheer over it or something. Both your Rayna and Sunlight have low or medium light requirements according to OrchidWiz. Especially Rayna as 70% of its parentage requires low light, 30% medium light so it needs shaded to dappled conditions. For Sunlight, it is 57% med, 25% high and 13% low light. Tropic Tom is a mix as well at 38% high, 35% low and 11% med light.
They all should be watered well and then just as they are beginning to dry out, water again. Usually when they have been shipped bare root I would keep them out of a lot of light anyways for a week or so as they will be struggling to adjust and should not have any extreme conditions.
I hope that helps. I find most of my oncidiums do not want to get thoroughly dry like I do to my cattleyas. Using a kebab skewer left in the media near the centre of the pot is a good way to tell when its time to water. Pull it out and feel it (on your upper lip or cheek is a good place to really tell how it feels) and then place it back in the same spot to avoid poking holes in the roots all the time. Good luck and welcome back to the orchid craze
Hybrid Mode
