I picked this up a few years ago in a collection of postcards I bought online. The card is postmarked 1960 from Sarasota, Florida. I learned the following from The Circus Blog:
La Fontain was their stage name. They are from the Canestrelli family, an Italian circus family. Tosca is on the right and Chi Chi is in the center. The last time they worked together was on the Hubert Castle Circus in the 60’s.
If anyone out there knows more about the La Fontain Sisters, please let me know.