I wouldn't think twice if someone who wasn't Arabic used the name. The first person I think of when I hear the name is
Farrah Fawcett who wasn't Arabic. Plus, it's close enough to names that are familiar in English, such as
Sarah,
Clara, and
Cara, so I don't think that using Farrah/Farah would be all that problematic. My guess is that most people in English-speaking countries aren't even aware of
Farrah's Arabic roots.
I'm used to seeing
Farrah, but I think I prefer
Farah. The additional "r" looks a bit superfluous to me. With that said, people might be more apt to spell it
Farrah due to
Farrah Fawcett, so going with
Farrah might be the better choice.
I would expect to see something more popular paired with
Jacqueline or something less popular paired with
Farrah, but sibling names don't have to match perfectly, so I'd say that
Farrah and
Jacqueline work as sister names.