The soil should be kept moist at all times, but not soggy. A rule of thumb is to place your finger down into the soil about knuckle deep. If it feels dry, then it is time to water. Remember that it rains a lot in the tropics, so they will want more water than the average house plants. During the winter it may be necessary to water more often.
Humidity is another important thing.
If it is too dry that is bad for the plants. You can spray mist them a couple times a day and that will help. You could also have a humidifier running to add humidity to the plants. I have been growing tropical plants for many years now. I have found that they can survive indoors.