A land transaction may be between father and son, sister and brother, or group of siblings and a remaining sibling. The document itself may not indicate any relationship among the individuals. The purpose of most legal documents is not to provide evidence of relationships. And in the case of a deed, it is to transfer title to property.
Everyone at the time the deed is drawn up knows how all those people are related. They never dreamed in one hundred and fifty years someone would be trying to figure that out!