Just one poison is usually enough.

Depends on the overall damage that's already been done by the caterpillars, but I'm a big proponent of finishing what you start. You have this much invested in the plant(s), are they worth trying to save...?
If light damage, get some vegetable-safe bug spray and follow directions on the bottle. Raise lights, apply the poison to entire plant (undersides of the leaves, too) and soil, wait an hour or two, rinse the plant with properly ph'd water, lower the lights. Repeat as directed. I'm not sure what it's lifecycle is, but the eggs will keep ya busy. Do not overuse the poison. it will cause as many problems as you're trying to solve.

I'd look into a different source for your potting mix, as that's the likely vehicle that brought-in the caterpillars and their eggs.