Just wanted to give a thought on the text I updated to bold type. I noticed this to, thought it was somewhat strange. That is until I started to think what kind of a person Lady Ashvane was. She was using her position to further her power and rank in Boralus, KT and the Proudmoore court. I think this was meant to be a simple visual device to show how Lady Ashvane has benefited from her position and machinations. That she had a greed for power rather than the simplistic view of "oh shes fat and therefore must be evil"
As for your baseline question. No. I dont. I think they used the models they did so the Proudmoore family would have a uniform look. In reality are all families bodies the same? No. But (and off into the weeds we go), generally speaking what your parentage looks like, is how you will look like due to simple genetics. Jaina has been somewhat slim from "GO" in this game, and she has gotten more... soft lets say, over time. But it informed the player base's expectations of what the rest of her family would look like.