You need to determine the era of manufacture and judge the condition. A large bookstore would sell a book on grading Barbie dolls. Considerations: Are arms, legs, head moveable? Type of eyes/hair? Original box / clothing? Barbie collectors have a nationwide organization. Consult MULTIPLE knowledgeable sources to determine value.
You can go to a doll show. There are always appraisers and buyers there. There are also local collectible shops that deal with dolls who will do appraisals or you can buy a book on doll collectibles and it will give you a good idea of how much your dolls might be worth.