Yes, the "Two's Family" situation is definitely a meant to illustrate Murata's thesis in a more everyday setting. Yoshiko and Kikue are bucking both the social expectation of heterosexual marriage and the expectation that your life partner is someone you have sex with, and it makes people around them uncomfortable.

It's sort of the inverse of the other stories? Rather than obey a custom that many readers will consider bizarre, the characters are bucking customs that many readers will consider "normal."

Thematically the collection shares a lot of preoccupations with Convenience Store Woman, especially the idea that people struggle to understand and accept anyone who doesn't fit their preconceived identity boxes.