Three in one container? Choiysa (Mexican orange) is an evergreen shrub that gets to be about 9' tall by 9' wide. Even if they are small now, I would get them into separate containers before their root systems get too entangled and give them enough room to grow.
I only know it as a plant of desert SW. I imagine you are over watering (probably if you are watering at all). It is very drought tolerant, but requires good drainage and does not like to stay wet.
If your potting soil in the containers has Miracle Gro or something in it, I wouldn't fertilize them at all until next spring. You don't want to stimulate a lot of tender new growth now with the growing season winding down.