Yosef Karo, Shulchan Aruch — Choshen Mishpat 36
“ If a relative or someone otherwise disqualified is found among those that intended to testify, their testimony is void even if they were not aware of each other. If all of the witnesses were valid- both those that intended to testify and those that did not but happened to see- and their testimony conforms, we would rule based on their testimony. ”
