Joao had only two surviving childrens by Catherine of Austria: a daughter, Maria Manuela (first wife of Philip II and mother of Don Carlos, Prince of Asturias) and a son John/Juan/João (husband of Juana of Spain, the younger sister of Philip II and father of King Sebastian).
OTL Don Carlos died unmarried and so without heirs before Sebastian’s death. If he had left descendants, something likely to happen if Mary of England’s death had not pushed the French to offer Elisabeth of Valois as bride for his newly widowed father instead of marry her to Carlos as was originally decided.
Hmm interesting. So, if we go with Mary living until say 1570ish-perhaps with better health and no shit showing from her father?- we could see Carlos and Elisabeth de Valois marrying, perhaps Carlos doesn't go as mad as he did otl? Or if he does and still dies, if he leaves one or two children before then that should be okay?