Are you trying to create a spread specifically for you in this thread (in which case you already know the ancestral line) or a spread for others to use? I thought from your original post that you were looking for help creating a spread for your personal situation.
If it's for others, something as simple as doing a pre-reading reading using court cards or something could be one way to pinpoint the ancestral line. e.g. Cups and Pentacles for maternal side; Swords and Wands for the paternal. Or something like that. Perhaps, it could be done with a second deck that you've already set aside the court cards for this exercise. That way you don't have to reintegrate and shuffle court cards back into the deck you're going to do the reading with. The court cards could tell the ancestor's gender and age.
Both. I wanted to create a spread that could be used to help in the discovery of where trauma exists in the ancestral line and how to heal it; maybe because I am still a novice, it seemed that such a spread could easily be used for trauma that is already known about to some extent. The pre-reading reading sounds perfect for this spread. I understand using the court cards to determine which side it takes place on, but how do they determine the generation or age of when the trauma occurred?