The way I tend to approach it is by modelling the desired cloudshape in Houdini, then use that mesh as spawnposition for various soft and hardedged textures on sprites to get a nice mix. In some cases it’s necessary to color the clouds based on vertexcolor of the emission mesh. Sometimes it can be done by using lights. It all depends on the usecase. Another thing to watch out for if you are going to fly through the clouds is not having such large sprites that they visibly rotate to face you. Often, locking one axis can help with this.
This was the technique used to create this scene (Not in unreal however):
These clouds hold up well enough to fly around and even through. They are not perfect but it’s a starting point 