Oooof! bugs/mites galore & not enough light.
My recommendation is to submerge the plants in a large bucket of water with a dash of dish soap. Not much. You want to first remove the soil from the roots GENTLY while they are submerged. Get rid of the dirt and water, rinse the bucket, fill again, but this time put a dash of kelp or seaweed extract in there. Not much. let the plants stay submerged for a bit in the kelp solution. ten minutes tops. use the kelp water to water some evergreen plants outside, or freshly planted flowers. Whatever. Great for roots and general plant health.
Next, make a potting mix that is a bit more free draining. I like to mix potting soil with Permatill (puffed slate granules) but anything that will add some drainage is good. get the dirt wet with more light kelp solution, then plant your iboga plants in pots that allow for more root growth. Put them in a warm, humid spot that gets significantly more light, but NOT direct sun yet. The plant has to have substantial woody growth before it is ready for more than morning direct sunlight.
If possible, keep them outside when the temperature is above 50 deg Fahrenheit. Being outdoors keeps pests at bay better because of the homeostatic nature of other critters. Indoors, the leaves will fall off way more easily. It is a defense strategy to reduce harm from losing too much moisture in a dry indoor environment.
Stake them up a bit, or if you have a few growth nodes on the plant, cut the leggy first internode of the stem off with clean clippers.
That's the basics. Let me know if you have any other questions. I've been growing iboga in a non-tropical climate for over 15 years now. Basse'