Tropical house plant problems?

Still sounds like a watering problem. Are you letting the soil dry out before watering? Most of the plants you mentioned react poorly to overwatering. Let the soil dry out until the top inch feels dry when you stick your finger in it, then water with room-temperature unchlorinated, unsoftened water until it runs out the bottom of the pot. Don't let them sit in a saucer of water, and don't water again until the surface is dry again. With a clean blade, cut off all the black, brown, soggy, or crispy growth--it will not revive. Don't feed them, because they're already stressed. If they have root rot, they may not survive. Don't move them if they're getting the correct amount of light, and don't expose them to drafts. The peace lily and orchids won't flower constantly anyway. Hope this helps...