Houseplants Dying?

I would agree they will probably have to go into different posts with fresh potting mix. I would try to do this outside if possible. You can spread the old soil on a baking sheet and let it bake in the sun but do not use for several weeks (if ever). New pots are better but you can disinfect the old and maybe it will help.

Maybe you can spray the entire plant with a weak solution (1 Tb to a pint of water or weaker) of Dawn blue (original) dish soap over the next few weeks but try to place them away from where you originally had them into areas that are recommended for each plant. Gauge light, moisture and especially air movement for each plant - just try babying them for a while.
Not sure about the moths but there are some that attack plants so you might want to Google moths (and color) in house and see what comes up.