This is one of my favourites. As usual face expressions are there, there is some narrative and you get to understand what is going on with every character. I would try to establish a conection between the sisters earlier, cause the older one it seems like she is looking for a rush for some reason, getting close to the younger one, and when she finds whats going on her reaction is too accepting.
The younger one has a better development cause her "curiosity" is aroused, and she takes more risks the hornier she gets, but she does it on purpose while the older one just happens to meet her. I would make her figure it out earlier and have a litle more buildup betwen them
Its apersonal opinon.
As for renders i would include some more renders,specially where there are transitions, cause it goes a little too quick from one thing to other that is quite different. Its still very good as it is, just not magnificient.
The second stage lacks a little contact, doesnt have that story progression stuff to the climax, so it has to rely on the quality of the actual sx scene that is still hot, but not as effective as the first part because of the lack of story.
What im missing in that scene is some more interaction. In a real sex scene is hard to put someone in betwen 2 people having sex, but still fantasy images do allow stuf, that i am missgin here. There are not many choices due to the sex position they chose and the environment, but i miss the older one doing more in some moments.
Its just Small details, it is still one of the most fappable content, if you like it. It just feels one step away from being the absolute masterpiece.