How many of you think that Jace is realated to Hodge Starkweather, and more than one family?
Well here is my theroy. If you've read the Infernal Devices then you would have known that Aloysius Starkweather had a grandchild named Adele Starkweather but that wasn't his grandchild. The Faries had switched the grandchild with a human child that looks just like his grandchild going by the name of Elizabeth. Adele had die while getting her first rune.
Eleizabeth had grown up not knowing the Shadow World and married Richard Grey then had a daughter; Tessa Gray, but Tessa was not Richard's child. Mortain had found Elizabeth and had a demon take Richard's place to get Elizabeth pregnant.
Tessa grew up also not knowing the Shadow World until her brother Nathaniel left to London where he met Mortain and had the Dark Sisters train Tessa into becoming a person with her powers. Due to the human deaths, the shadowhunters investigated in who is responible. Will Herondale saved Tessa while he was on the invesigation but as time grew they both fell in love.
After Tessa and Will had a child; James and Lucie, James married Cordelia Carstair and Lucie married Jeese Blackthron. James and Cordelia had a child named Owen that married Lydia Kingmill who had Marcus Herondale that married Imogen Whitelaw who had Stephan Herondale who married Atamis Garroway but divorced her because Valentine didn't approve of her then married Céline née Montclaire who had Jace Herondale. Also Cécliy Herondale married Gabrial Lightwood and Giedon Lightwood married Sophia Collins.
In conclusion, Jace is realted to the Starkweather, Grey, Carstair, Blackthron, Whitelaw, Kingmill, Garroway, Lightwood, Collins and probably more.
If you agree than look up more people that is related to Jace.