[Opinions] Re: Nicknames?
Short answer: Anything goes as a nickname, so yes.
Long answer: If you're wondering if they're intuitive nicknames, the kind that won't make people outside the family wonder "where did that come from?," Piper, nn Pippa, feels more natural to me than the reverse. Emery for Emerald is fine, but the J in Jem throws me a bit. Gem makes more sense to me. Jewel could work too.