SOLVED. Three sisters with names meaning "light" [s]

[Malin]

Looking for a book I read when I was in elementary school in the late 90s/early 00s.

The main character, a girl, goes to live with a family with three daughters. The names of these three sisters are Lucy (which means "light"), Helen ("torch") and a third name that also means something like "light" (Clara perhaps?). The name theme is explained to the main character when she first meets the sisters, and that is the only concrete thing I remember. There was a mysterious air to the story, I think. It might have been a historical novel, or maybe the sisters' family was just old-fashioned?

I hope these "light" sisters sound familiar to someone, because this has been bugging me for ages.

[Malin]

Ooh, that is definitely the right book! I did have a vague feeling one of the sisters was named something unusual, but I was so sure there was a Lucy. Probably mixed it up with Narnia which I read at the same age. It seems it was released in Swedish (which I read it in) in 1998, so that makes sense. Thank you!