I've never met an
Elisa, but I would tend to pronounce it like you, eh-LEE-sa. But even while doing so, there would be a question in my voice, as I'd already be second guessing myself. Personally, I think that's the way is should be pronounced, as it needs the double consonant so turn it into eh-LISS-ah. But, well, we've all seen what creativity has done to naming, so who knows anymore.
Ian...EE-un, two syllables.
Brittany...BRIT-nee, two syllables.
And I'm in central Canada.