First off, welcome to OB! You're gonna love it here.
Also, congrats on your keiki! If it were my plant, I would repot the mother plant as needed and leave the keiki until it had sufficient roots, like you proposed in your question. My thinking is, the mother plant needs to be as healthy as possible to sustain itself and the keiki, and repotting is so important for maintaining healthy roots.
As for your other combo plant, I would gently repot it once you get your new supplies. It may not adversely affect your flowers anyway, and you'll be able to assess and protect their root health. I would separate the plants into two pots.
I'm a windowsill grower too, and I've used both Superthrive and KLN in the past for strengthening stressed or root-poor plants. In contrast, I have a bottle of Physan that I bought "just in case", and I've yet to use it. But just go with whatever you want to try, because there are so many ways to go about growing orchids!