What did the
German site say its origin was?
Cyneburga is Old English, like this website says. Hopefully someone can answer the rest of your questions better, but I do know that Old English comes from Germanic (then had a lot of Old French influence).
German is also from Germanic, just on a different branch. If you look at a language tree it makes more sense. Like one of these:
http://andromeda.rutgers.edu/~jlynch/language.gifhttp://www.vaughns-1-pagers.com/language/euro-languages.gif