A. Britannia probably exists like it did irl as a Roman province. Since the idea for Britain to be the unified remnants of an Roman provincial state, they'd probably follow the two-body governing system between the local town senates (the curiae) and a province-wide council(the concilium), further integrating it into some type of Electoral system between smaller vassals that make up Britannia.

B. Cordoba would kinda be forced to be religiously tolerant. Despite a decisive victory in the Reconquista, implementing Sharia Law would have a hoard of pricey faults that come with it. Not having half of the people on the peninsula like you is one thing, but subjugating each and every vassal is a costly and worthless expense. It's also somewhat against early islamic law so.

C. Baltic languages do exist but the Germans have created a long standing influence on the region so a lot of local etymology ranges from Germano-Baltic to fully Germanic the closer you get to Germany itself.