Since the beginning of the project, many trainees left the agency. On September 1, 2018, it was announced the departure of three trainees of the agency, two of them being the finalist of MIXNINE, Lee Somin, and a trainee who appeared in Produce 101, Park Soyeon.
On October 18, 2018, the agency announced the pre-debut showcase of the group, titled WE?, to be held on November 11, with the official members.
Starting on October 21, the official members were being revealed day after day via social media accounts. The first member was Lee Soojin, followed by Monday (who was not a part of the original project's line-up), Park Haelin, Shin Jiyoon, Park Soeun, Kim Gaeun and finally, on October 27, the last member, Lee Jaehee, was revealed. 
In July, 2019, trainee Park Haelin announced that she parted ways with PlayM Entertainment and the project to focus on her studies. In October, Kim Gaeun also left both the agency and the group.
|Lee Soojin (이수진)||Main Dancer, Vocalist, Rapper||2018–present|
|Shin Jiyoon (신지윤)||Lead Vocalist, Lead Dancer, Rapper||2018–present|
|Monday (먼데이)||Main Vocalist, Lead Dancer||2018–present|
|Park Soeun (박소은)||Lead Vocalist, Lead Dancer, Rapper||2018–present|
|Lee Jaehee (이재희)||Lead Rapper, Vocalist||2018–present|
|Han Jihyo (한지효)||Lead Vocalist||2019–present|
|Cho Hyewon (조혜원)||Main Rapper, Visual, Maknae||2019–present|
|Park Haelin (박해린)||Leader, Lead Vocalist||2018–2019|
|Kim Gaeun (김가은)||Main Rapper, Vocalist||2018–2019|
- Several girls from the pool of trainees were present on reality competition shows in order to increase the girl group's pre-debut popularity:
- Park Soyeon was a contestant on Produce 101. She was eliminated on the episode 11 after ranking 18th place.
- Trainees Baek Minseo, Kim Bowon, Lee Soojin, Lee Soomin, Park Haelin, Park Soeun, Shin Jiyoon and Shin Suhyun were contestants on MIXNINE. Only Lee Somin made it to the final line-up after ranking 9th place, but was eventually eliminated along with the girls team.
- Shin Suhyun became a contestant of another reality survival show, that being Produce 48. She ranked 61st place in episode 5 and was eliminated.
- ↑ Allkpop: FAVE Entertainment Announces Departure Of FAVE Girls Trainees Lee Soo Min, Kim Bo Won, & Park So Yeon From The Label
- ↑ Soompi: FAVE Entertainment Announces Plans To Debut New Girl Group
- ↑ Soompi: FAVE Entertainment Reveals Final Trainee Of FAVE Girls Debut Project
- ↑ Produce 101: Episodes 1-11
- ↑ MIXNINE: Episodes 1-14
- ↑ Produce 48: Episodes 1-5