、。
Strange as it seems, none of us noticed the mistake.
Literal
Strange story but [concessive-が], we [topic-は] anyone [even-も] that mistake [on-に] didn't-notice.
誰も ... ない ('nobody ... at all') — 誰 ('who') + も + negative is the universal-negative pattern. Combined with 我々 at the head, the sentence first sets the group and then says 'none within that group.' 気付く ('to notice') takes the noticed thing with に, not を.