"Sister city" "Brother city" "Sibling city" "Twin city"

For some strange reason, no one ever says "brother city." The term "sister city" is very common. "Twin city" is also conventionally used. I do think it's a bit strange to say "sister city" but not "brother city," and it forces me to think about gender in a context where I do not want to think about gender. So I like the term "twin city" better. "Sibling repo" preferred to "sister repo" for the same reason (if I was reading this Github documentation, having to think about a repo as female gendered would be a highly distracting diversion while I'm trying to concentrate on source code).

I’m truly not trying to be obtuse when I say that not only does it not force me to think about gender, it doesn’t specifically evoke gender for me at all. Our radars seem to be calibrated differently. It’s often said that to seek offense is to find it.

Laughs in French

By the power of Greyskull, this sounds like a job for Theyperson and Theyra.