Hi MarionJ. That’s an excellent question, and there are a few ways you could approach this.
One option is to store your character sheets and other items on your computer’s hard drive and then use external links from each book’s Scrivener project to those materials.
In the Scrivener manual, §9.2 discusses using the File > Import > Research Files as Shortcuts option for accessing those materials.
However, you could also set up one Scrivener project that’s specifically used as your series bible and then link each book to that project as needed.
On the forum, our Head of Support uses AmberV as his forum handle. He wrote up a post on using one project for general note-taking, which you might find useful. He includes some links to other discussions on the forum as well.
Also, our Outreach Specialist Oliver had a webinar on this topic on August 28, 2024. Those videos are usually available for a couple of months. You can see that replay on this webpage.
Those should give you some starting points for considering your options.