Christina seems dated to me.
Norah definitely does not seem dated.
Sarah kind of does, because I was born in 1987 in the US and grew up around a bunch of white kids. However,
Sarah is classic and sounds fresh to me on children now, whereas
Christina just sounds dated on children. For siblings, I would say that
Sarah &
Christina together are dated - those sisters can really only be in their 20s in my opinion - but
Sarah &
Norah or
Norah &
Christina don't sound dated as combinations.