If there are two people assigned an Account Certification role, will we both be assigned the Account Certifications?

Yes - When multiple people are assigned to a Role on any worktag (e.g., Grant, Cost Center, Gift, Project, etc.) that is affiliated with Account Certification, they all are assigned the corresponding Preparer/Approver role for the worktag.   Any person assigned the Account Certification can take action (submit).  Once action is taken, the Account Certification will be removed from all Preparers/Approvers Account Certifications Awaiting Me table.