It would be two. Perez and Zerah and Jacob and Esau...do not know about Thomas. James and John, sons of Zebedee were brothers - they do not specify if they were twins. The were called "Sons of Thunder"
I know of two pairs of twins in the bible Jacob and Esau, and Thomas and his twin.
Perez and Zerah-twins of Judah and his daughter-in-law Tamar