Sounds like your Ficus Elastica aka rubber plant aka rubber tree is suffering from overwatering.* This could have started before you purchased it.* The clues for me are the combination of falling leaves and the brown tips.* It's best to let the top 2" of soil dry before watering.* If it's not too rootbound you can stick your finger into the soil up to the first knuckle to see if it's dry.* Over time you will just know how often to water.* Never let a houseplant sit in water in the saucer for more then 15 minutes.* If it continues to drop leaves and looks unsightly you can start again by air layering, cutting the main stalk and rooting it in soil or perliet, using a cutting from the stem aka stem cutting or taking cuttings of the side branches and rooting in either perlite or moist potting soil.* The propagating soil should only dry out about an inch below the surface until roots have formed.
Here's how to propagate houseplants.
It's best not to fertilize a stressed plant.* If you feel you must fertilize, it would be best to use an organic fertilizer such as fish emulsion with sea weed.* That will gently feed the plant.* Synthetic fertilizers contain residual salts that plants don't need and are like sterioids for your plants.* Best to feed gently.
Sounds like the bugs in your caladiums are fungal gnats.* They certainly are pesky, but tend to be harmless unless they are in large quantities.* They are attracted to soil that is kept too moist. Slices of potato can be helpful in getting rid of them.
You can also make an alcohol spray for the soil only.* DO NOT SPRAY ON YOUR PLANTS.
Mix four parts water with three parts rubbing alcohol into a spray bottle. Spray the mixture around topsoil and infested areas.
Sticky traps also help.* Here's how to:
More natural remedies for insect pests.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.