This is the first year my plumies stayed outside in a greenhouse and not be brought indoors. I keep the heater on inside and it doesn't drop below 55º inside at night. It is much warmer in the day. But they are acting weird. The bottom leaves have yellowed and a bunch have fallen off. Yet there is new growth on the tops. Some are not losing leaves at all : The pudica look good and the pink pudica looks great. I also have a white(?) noid that is not dropping leaves at all and the Riveria Rainbow is also pretty green, though it's broken babies in a separate pot are naked. What causes this irregular non-uniformed leaf drop?

You will find that certain plumeria are much less prone to dropping leaves than others. My Riviera Rainbow tree will not drop its leaves at all until late winter when they all drop at once and new ones will start appearing almost immediately.Your no id. white might be a species. There is no rule for leaf drop!
The new growth at the tops is probably caused by warm days. I am seeing this here too.

Hetty, after a week my two varieties of plumeria seeds are showing no sign of growth. Anything I should do to "jump-start" them or just remain patient? I was told to put them all in a baggie, but they are on the wet paper towels, on a tray, and covered with cellophane. The paper towels have stayed wet since I prepared them for germination and I am quite sure the humidity in that tray is pretty much 100%.

Thanks for the explanation @Dutchlady Hetty. I have an orange NOID that is looking quite stunning actually. LIke it never saw the likes of winter.