A family tree that traces blood relations (consanguinity) is relatively easy. In this current age family trees are complicated by multiple marriages, divorces, children born out of wedlock, step-relations, half-relations, and adoptions. Biological lines are mixed with paternal lines in defining family. In establishing criteria for this family tree, one has to weigh factors such "revealing family secrets," offending, and truth. Although there is no intent to offend or hurt anyone, this family will try to use "truth" as the primary criterion.
When life's decisions are based on false information, the decision maker is at a disadvantage in making the best decision is a lesson learned by many of us. That is primary reason that "truth" will be used as the primary criterion.