I posed my "two many brothers" question (ha ha) on the Writing Workshop chat list and received some feedback. Of those who piped up, the general consensus seemed to be that, yeah, two pairs of half-brothers IS one pair too many and I should drop the more minor pair of characters, or steal their plot arc and use if for the hero.
Good advice, although it won't work in this case.
Anyway, I brainstormed some more and came up with new ideas.
My character is back to being an only child. But, he is a member of a fraternity. Is there a word for fraternity which includes both boys and girls?
The Thesaurus just gives me: "Brotherhood" (obviously no improvement) and "affiliation, camaraderie, club, confederation, congress, federation, fellowship, frat, guild, house, kinship, order, sisterhood, society, sorority."
I don't want to use "secret society" because I use that in Dindi a thousand times. I want a word with more meat to it than "camaraderie", less Lord of the Rings than "fellowship", more class than "gang", more youth than "order" and more substance than "affiliation." "Kinship" makes no sense. "House" is weak, although perhaps it is used in English for what I have in mind. Guild isn't quite right but I'm leaning toward it by process of elimination right now.
"Sodality" is cool, Maybe a tad too exotic?