Hi, Brad.
It could be a number of things, but let me make a few guesses.
First, it could be the change from outdoors to indoors.
Second, it could be over or under watering.
Third, it could be a nutrient deficiency.

Generally, the oldest leaves will be the first to show nutrient deficiency,
so I'm leaning in that direction.

If you're sure that the plant isn't too dry or too wet, you might try a mild fertigation.
If you notice an improvement, hit it with another mild dose after about a week's time.

Josh

Thanks, Josh!

I read in a magazine somewhere that you can give your plants a boost by giving them unflavored gelatin! I'm going to have to find some to try it! Of course, for now, I think I'll give them a little fertilizer.

On australis, it's two cuttings that are yellowing and obscura has random yellowing leaves. Sounds like I'm going to have to get some VF-11 here soon!

Brad AKA Moonwolf

You're welcome, Brad.
I'd go for something stronger, personally.
VF-11 is a very, very mild tonic, and probably best for maintenance.

I'm a fan of Foliage Pro 9-3-6, which includes all of the minor nutrients, as well.
It can be difficult to locate, but I use it on everything...from Hoyas to Hedge-apples,
Jades to Maples, and even in-ground plants such as hot peppers.

I seldom use more than 1/4 teaspoon per gallon of water.

Josh

I've been using Miracle-Gro Tomato Fertilizer since early in the growing season. Would something like that hurt them this late in the season? I also have MG Houseplant Fertilizer that I could use on them. It's a liquid.

Brad AKA Moonwolf