Final answer:
No, the statement is false. There were female instrumentalists in Sly and the Family Stone, including keyboardist and vocalist Rose Stone and trumpeter Cynthia Robinson.
Step-by-step explanation:
The statement is false. While the backup singers of Sly and the Family Stone often included female members, there were also female instrumentalists in the band.
For example, Rose Stone, who was one of the original members of the band, served as a keyboardist and vocalist for Sly and the Family Stone. Cynthia Robinson was another female member who played the trumpet. Therefore, it is incorrect to say that the only female members of the band were backup singers.