Not for me but

[34AQuid]

Isabella and Gabrielle? Too matchy matchy?

I think they are too similar for siblings.

I think they are just about okay. Love both names. Also depends on the nicknames. Bella and Gabby are fine together I think, as would Izzy and Gabby.

I think they're fine, as they're not likely to be called their full names by other people.

Isabella seems to inevitably become Izzy or Bella. Gabrielle always becomes Gabby. Gabby, Izzy and Bella are not similar at all, so totally fine.

People might get mixed up over which one ends in '-ella' and which one's the '-elle' but as PP said, they'll probably have nicknames anyway and those don't sound too matchy. :)

I don't think they're too alike but I think people would mangle them. You'd have people asking after Gabriella and Isobel.

I think they're fine together