Follow me here, i just had a lightbulb brain moment!
CASTOR's Original DNA comes from Abel Johanssen
We are assuming that Abel is the biological child of Henrik and Bonnie JohanssenÂ
We are assuming that Gracie is also the biological child of Henrik and Bonnie Johanssen
CASTOR and LIDA are brother and sister genetically
So, does this mean that Gracie was implanted with her sister's (Helena) egg that had been fertilised by her father's sperm????
And that Gracie, who married Mark, a CASTOR clone - actually married her brother??
Either way i look at it, Gracie is at least the half-sister of CASTOR as well as LIDA...