By a supersingular Abelian scheme, I mean an Abelian scheme which is fibrewise a supersingular Abelian variety, i.e. isogenous to a product of supersingular elliptic curves (F. Oort, Subvarieties of moduli spaces. Invent. Math. 24 (1974), 95-11995–119).
Let $\mathscr{A}$ be a supersingular Abelian scheme over an integral variety over $\mathbf{F}_p$. Is it true that $\mathscr{A}$ is isogenous to a product of relative elliptic curves over $X$? I am looking for a reference. Equations (0.4.1), (0.4.2) in [Li-Oort, Moduli of Supersingular Abelian Varieties, LNM 1680] seem to imply this.