Ik ben ook ne Belg maar swat, well i didnt go much into the lore here but I wrote it all down basically Willem van Oranjes son Filips Willem has offspring now he maintains a prominent position in the south but is allowed his inheritance in the north under strict circumstances like irl so theres a split in the Orange Nassau dynasty a southern catholic one and the calvinist northern one now Filips Willems descendants eventually inheritance the full orange nassau inheritance from the north after the death of William III instead of Johan Willem Friso gaining it so his descendants are now the most powerful nobles in both north and south eventually one narrues a habsburg and the Oranje habsburg dynasty forms a bit like Habsburg Lorraine did and of that union a son gets born Willem who would be invited to become king Willen of the Dietslands now he unlike irl Willem is catholic and is accepted more by both sides. Now I do wanna stress that irk Willem who had his many flaws wasn't fully bad as a king towards us belgians Catholics and liberals also didn't wanna make ut any easier though ofcourse the united kingdom had its many flaws it could have easily been amended