Legal Question in Business Law in California

I'm not clear on whether what you're proposing to do is to make copies of the character charms or buy charms made by the copyright (or trademark) holder and incorporate them into your jewelry. The former would be a copyright violation; the latter possibly a trademark violation because even though the charms would be "authentic" (made by the trademark holder or with its permission), the incorporation of them into your product could be considered "trademark dilution" which is a form of violation often recognized by the courts.

In either case, avoiding infringement would almost certainly require more than indicating the source of the material....giving credit does not go far enough.

I recommend figuring out who holds the intellectual-property rights (trademark and/or copyright) or who speaks for its holder, describe what you plan to do, and ask whether permission is required and, if so, may you have it. Get it in writing.

No, you can't get around infringement just by saying "inspired by." If these are popular characters, it is likely they already are being made into charms by a licensee of the owner of the characters. If you want to do this as a business, you should behave like a business person and approach the owners of the characters you want to use and obtain a license. If they won't give you a license (because someone else already has it), then you can't use them.

Usually, a license would require that you give the owner a fee up front plus a percentage of what you make on the sale of your charms. If you don't think your sales will be worth that, then don't do it.