Describe what they look like (leaves turn yellow, leaves fall off, stem rots, has bugs, etc.).
Are your plants root bound? Pull plant out of pot and inspect roots, if the roots are coming out of the pot or are not surrounded by soil, it needs to be repotted, to the next size up.
Most house plants die because of incorrect watering usually over watering. They need extremely bright light usually not direct sunlight. That being said we need a little more info. may be some pictures,are they in windows(too cold),drafts(too hot too cold)certain colored spots on leaves(fungus),bugs??? so many things