Number refers to the legally prescribed complement of witnesses; integrity refers to their trustworthiness and moral fitness.
If the applicable judicial proof requires two qualified witnesses, one exceptionally upright person does not fulfill the number requirement. Likewise, producing enough persons who do not satisfy the required integrity standard is not enough.
The source relates these ideas to expressions such as «واستشهدوا شهيدين من رجالكم» (“Call two men among you as witnesses”) and «وأشهدوا ذوي عدل منكم» (“Call upright persons among you as witnesses”). Specific evidentiary configurations remain governed by the detailed rules for the case in question.