Keep them wet? Why? Being a 'raintree' doesn't mean it likes wet feet any more than any other tree, though it shouldn't be allowed to dry out (nor should the Serissa, but that can take a bit more drying). They are probably missing humidity like mad, and the light they had outside. Keep them away from any heaters, and put the pot on pebbles in a wide tray of water - just be sure the water's never high enough to wick back into the pots and rot the roots. Give them as much light all day as possible (a good full spectrum fluorescent 6 inches away for up to 16 hours daily will do it) and let them adjust to the changes, but don't just water 'because it's Wednesday' or anything - wait til they're just starting to look a tad tired then do it, but make sure your mix has lots of grit in it to allow water to drain quickly. I wonder if the leaf drop wasn't a reaction to being out in weather cooler than it should have been (though Serissa especially can take quite cool temps for short times).