I'm not sure which couple is the least close but the closest couples are Yoonyul, Taeny, Jeti, Hyohyun, and Yoonhyun. Taeyeon doesn't seem to be as close with Hyoyeon, Sooyoung, and Yuri. Jessica and Sunny both seem to be less close with Sooyoung and Yuri. Sunny and Yoona aren't that close and Jessica also seems less close with Hyoyeon. Same with Fany.