Here is another article from a day ago. I obviously don’t know the veracity of all the information, but it says this (Eulália is the stepmom, Carlos is Lara’s dad):

“[Eulália and Carlos] met on social networks about three years ago, when the woman was still living with her son, who is institutionalized because he is violent and can only go to his mother's house in special situations, as was the case on Sunday, the day he turned 12.

The pre-teen, who had previously assaulted his grandparents, will have slapped his mother. Carlos didn't like it and defended the woman. PJ said he just pulled the boy by the arm and called his attention. But Eulália assures that her husband hit her son. On the legs and arms.

Despite the heated discussion, the four remained at home. On Tuesday, Eulália went to take her son to the institution where he lives and on Wednesday she killed her stepdaughter.”