II’m an OT/Hebrew Professor. You’re mistaken about the necessary reference of the singular pronoun in v. 27. As you note the antecedent (‘adam) is a collective noun (thus always grammaticlly singular, whether referring to an individual or group). If it’s is meant to be a group, then a subsequent pronoun could either be singular (to show grammatical congruity) or plural (to show conceptual congruity). Both are legit in Hebrew…only larger context can decide.
Also, be careful not to make too much of the article in v. 27. Though Hebrew is closer to Greek in the use of articulation, they are not identical. The article could simply be a reference back to the ‘adam in v. 26 (I.e., this ‘adam).