Answer: Based on your description, I am not sure exactly what is wrong with your plants but here are some suggestions. African violets grow from the center and as they grow new leaves, the older ones around the outer edge normally tend to fade and should be removed. The plants may also become crowded after a year or two and may need to be divided; in htis case the center becomes raised up and the outer leaves look unhealthy, too. Another reason can be that they need more water and/or higher humidity. If they have grown a lot, you may need to water them a bit more than you did at first when they were small.
Christmas cactus may drop some leaves if it is overwatered and having a root rot problem. If you have been keeping it very dry, it may be that it needs more water; despite its name, this plant actually needs water and humidity to stay healthy. You might try washing it in tepid water if it has become dusty and make sure to keep the soil slightly moist. To increase the humidity during the winter when the heating season makes the air so dry, try placing the pots on a pebble tray filled with water.
Finally, your plants might also have an insect problem, so check very carefully for any signs of insect activity. Be sure to look under leaves and where the leaves join the stems, and in the violets, look carefully around the crown.
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