Three producers are credited for Practical Magic 2 in the main film credits: Denise Di Novi, Sandra Bullock, and Nicole Kidman.
Denise Di Novi produced the original Practical Magic and returned as a producer for the sequel. Bullock and Kidman both reprise their roles as the Owens sisters and are also credited as producers. Their involvement therefore extends beyond acting.
Producer credits concern the organization, financing, and overall management of a film’s production. They are separate from the director, the screenplay writers, and the source novelist. Susanne Bier directed the sequel, while Akiva Goldsman, Georgia Pritchett, and Kelly Marcel are credited with the screenplay.
The answer is three because those are the names in the infobox’s produced-by field. Other people may receive additional executive or departmental credits in a production, but the main producer listing for Practical Magic 2 contains these three names.