Here's one site that has a ton of info on royalty. https://www.unofficialroyalty.com/

Here's one on the "They are all jews" theory. It relies on matriarchal lineage defining Jewish identity, it seems. Maybe someone familiar with that idea could comment, or on how "matriarchal" compares with "matrilineal." https://www.algora.com/Algora_blog/2018/02/01/the-truth-about-the-so-called-british-royal-family-are-they-a-ll-jews

Here is what I think fascinating, the hidden matrilineal line of Garsenda who was the mother of most European royalty. https://byteside.com/2020/12/game-of-house-garsenda-the-secret-matrilineal-power-in-european-royal-history/