Yeah, they were my big literary obsession before Harry Potter came and swept me away. They are children's books though, with protagonists in their pre- to early teens. So I don't know if you'd find that interesting? As far as children's literature goes they are interesting. I'd probably still enjoy them :)
I did a little Amazon search and it seems like two of them, the ones centering around the Irish siblings, were translated to English: Captured by Vikings and Escape from the Vikings. So you can take a look if you want :)