The more I read, the more questions...
There are some premades, including the Charm family. The elderly Minerva Charm is said to have a "Strong bloodline". I thought that she would then pass on the "Ancient bloodline" to her children, but both Darrel and Gemma have only the "Strong bloodline". I don't know who their father(s) are, but even if he had no bloodline at all, they should still be given their bloodline trait from Minerva, right? And - if Minerva was not an active Spellcaster at the time, then children should get a poorer trait, which would be "Weak bloodline"...
So, I don't get the logics, unless Minerva isn't the real mother to these two at all? Maybe she adopted them as she married their father(s)? I even suspect them to have different fathers, as Minerva's hair looks blond, Darrel's is brown, and Gemma's is black. Dyeing hair happens, though... (found another picture of her where the hair is grey and green, so genetics is no longer an issue...)