Answering your question: of course not.

Real World Terrain can create heightmaps, textures, and (if it's marked on Open Street Map) buildings, trees and grass.

If you need a beautiful river you can use something like AQUAS Water / River Set.
If you need fluid simulation, you can use something like Fluvio (not tested).
But in any case, this is not a built-in feature of RWT.

1) Import a map of a Caribbean island. This map I would like to include buildings, mountains(hills), and rivers(dept if supplied by google)

2) "Fill" the rivers, with water(fluid material) and have it flowing.

3) Can a fluid material be used as sea around an island.

4) Can I change the "material" of "slipperiness" of a part of a mountain,  to mimic a landslide.( Lets say change the mountain material to muddy and let gravity to the rest.

I don't expect your asset to "generate water" for rivers. but looking at many models in unity3D it only shows a blue waterline that represents a river but i want a real river or real area for the river water to run, where I can raise water levels and cause it to over flow flood areas.

Also Ability to edit "liquidity" of a selected area of mountain to mimic a landslide.

Regards