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John Luxembourg, duke of Goerlitz surprisingly died at the very young age (he was a younger brother of emperor Sigismund), supposedly from being poisoned. But what if he didn't? What if he did die aged 81 in 1451, alongside with his daughter Elisabeth. He and his wife were fairly young at the time of his death (and he was busy being at war before, which wouldn't be the case ITTL), so we could expect more children. Say that the couple has two surviving sons:
Charles (born 1397, named after Charles IV of Bohemia) Casimir (born 1400, he survives but his mother dies in birth as IOTL, named after Casimir III of Poland) Than we have turning point of year 1411, when Jobst of Moravia dies. John, being briefly Elector of Brandenburg before, would have a lot better position to claim Brandenburg than his Imperial brother. It'd improve the situation of him and his sons. Charles (who is undisputed heir to Bohemia after his father and uncle) would probably marry his cousin, Elizabeth. Meanwhile younger Casimir could marry Hedwig of Poland (daughter of Jogaila and Anna of Celje) - he is the son of the Elector of Brandenburg and emperor Sigismund wouldn't oppose the marriage because he would see a chance of House of Luxembourg getting both Poland and Lithuania (and he is older than Frederick II the Iron, who was Hedwig's fiance IOTL) and if marriage happens before Hedwig's death than Sophia of Halshany and her descendants could be easily butterflied (say that Sophia is among the persons who are going as a Vytautas's suite to the wedding, but she meets a bear in the Lithuanian forest and sadly doesn't recover from the injuries made by bear). @Jan Olbracht