I know there are a lot of translations where 庶 vs 嫡 bloodlines come into play. Looking for some thoughts on translating this so it isn't a mouthful every time. Specifically, I'm looking for a way to translate 庶房. The concubine in question is no longer relevant to the story as far as I can tell, so this is solely related to a concubine's son's branch of the family. 'Concubine-born branch' seems like a bit of a mouthful but it's the best I have right now. Looking for ideas for a shorter phrase.
Since you said the concubine was no longer relavant, why not just Branch Family? Why bring Concubine into it?
It's important to the story. This family has not split their household, so there are two legitimate sons with families, one concubine-born son with a family and one not yet married concubine-born son who marries partway through the story. The branches all existing in one household means that the story refers to them as the first branch, second branch and third branch. The third branch being a concubine-born branch means that family gets lesser responsibilities and money from the household, which is important to early conflict.
Differentiating them by calling them primary line versus secondary line seems to make sense. "Branch" suggests that the household has been divided but since that hasn't happened yet, it doesn't seem to quite fit the situation.