Yeah, I'm glad this isn't a banal as other harems. Actual plotting and effort put forth by all. That said, as a Miku first, harem second supporter; Yotsuba totally isn't out of the race. There'd be no way the development of all five of them wouldn't progress together. Pacing and focus wise they'll definitely have to be unequal. The race and their bonds as siblings are far too interwoven for any ship to truly end without having huge impacts on the bonds as siblings.