WRS said:
The wiki is correct that City Forest is the circle's name. It is likely that the site is primarily posted to by TAKTO; Tomori has an author page there but it's completely blank. There's also no links present for Tomori's socials as supposedly a member artist.
My opinion is to leave the tag as-is for posts that cannot be individually attributed to either artist, unless the majority of the posts belonging to city forest online are currently TAKTO's, in which case the alias can be approved and Tomori's posts can be moved out into a separate artist tag.
Looking at the tag currently after my attempt to garden it, the posts remaining under city_forest_online -takto are mostly Flower Knight Girl game CGs & official art done by takto and also one post for a character from Sengoku Rumblade. The posts I left under city_forest_online takto are mostly doujin covers that list the circle's name alongside takto's and the posts I wholesale moved over to takto was official art for VR Eroge Yattetara Isekai Ni Tensei Shita No De Bishoujo Maou Wo Doreika Suru ~Cross Out Saber~ and FKG doodles with their signature on it.
Slapping the website into the wayback machine shows that the sidebar used to say "CITY FOREST ONLINE は、都森/TAKTOのイラストとサークルCity Forestの情報を公開しております。" Tomori (都森) is no longer listed on the live version of the website, indicating they split. It looks like none of the art we currently have on here is by Tomori. Not sure why the email apparently for tomori is still in the site description though.