I don't understand. Instead of being family-less, Zhang QIling can simply become sworn brothers or maybe be uncle-nephew…
That is because Zhang Qiling and Zhang Rishan are from different parts of the clan Zhang (Qiling from the pure one, Rishan from the south) and these two parts used to have conflicted with each others. Also Zhang Rishan blood line was very much washed up from the pure Zhang clan, so they basically are not family at all. (all information is from the book)