I wanted to mention that your third Crassula arborescens 'Undulatifolia' is the selected cultivar Crassula arborescens 'Blue Bird', a much bigger and sturdier type overall. I think this was originally developed in Europe (or possibly South Africa) and given the Dutch name 'Blauwe Vogel' but it is more frequently seen as 'Blue Bird' nowadays. There is a known literature reference to this plant in the Bulletin of the African Succulent Society 6(2): 74-75. in the article "A note on a hybrid Crassula. (T. Lavender 1971)" but I haven't yet managed to find a copy of that journal locally to check on what it has to say about the plant, perhaps you will have better luck.
One of the things I really like about this plant is the colour of the maturing anthers - they are a deep violet blue which looks really neat
I am adding a close up photo showing this feature to this post.