According to Thomas Elpel in his fantastic book Botany in a Day (6th edition), there are 7 genera and about 220 species in the magnolia family.
I have spent considerable time exploring which species have edible magnolia flowers. Below is a list of the ones that I have found in the ethnobotanical record. It is by no means an exhaustive list.
Edible Magnolia Flowers
Edible Magnolia Flower Recipes
Hu, S. (2005) Food Plants of China. Hong Kong: Chinese University Press.
Kunkel, G. (1984) Plants for Human Consumption: An Annotated Checklist of the Edible Phanerogams and Ferns. Koenigstein: Koeltz Scientific Books.
Facciola, S. (1998) Cornucopia II: A Source Book of Edible Plants. Vista, CA: Kampong Publications.
Sturtevant, E. L. (1972) Sturtevant’s Edible Plants of the World. New York: Dover Publications.
Standley, P. C. & Steyermark, J. A. (1949) Flora of Guatemala. Fieldiana. Chicago, Ill.: Chicago Natural History Museum.