It does not matter whether they achieve the same Examination Mark. If they are not both ranked first, then the Assessment Mark of each student will be different. In terms of this particular example, the Assessment Mark of the student ranked first will be adjusted to equal the highest Examination Mark of any student in the cohort. If the student ranked first also achieves the highest Examination Mark, then their Assessment Mark will be the same as their Examination Mark, resulting in the same HSC mark.
However, this does not apply to the student ranked second. While the student ranked first and the student ranked second can achieve the same Examination Mark, the Assessment Mark of the student ranked second will most likely be lower than that of the student ranked first because of their lower rank.