Zil marriages are invariably preceded by an extended round of negotiations and prenuptial agreements that determine the details for each particular marriage. For most Zil, such bargaining and negotiation is part of the courtship and considered romantic.
— Keith Baker (@HellcowKeith) January 18, 2020
So would you see a Zil marriage negotiation that ends up with siblings having different family and house names from each other? It's certainly possible. In a Sil/Lyrriman marriage, the contract could stipulate that both spouses take the Lyrriman name, but that the firstborn child will be legally Sil. It can be as complicated as the spouses and their families want it to be.
— Keith Baker (@HellcowKeith) January 19, 2020