A preabelian category is called *integral* if epimorphisms are stable
under pullbacks and monomorphisms are stable under pushouts.
A major property of integral category is that by inverting bimorphisms one can turn it into abelian category.

Is it true that the category of abelian varieties over a finite field is integral with bimorphisms being isogenies? If yes, could you give me a relevant reference?

The same question about the category of $p$-divisible groups over a finite field of characteristic $p$ and over the ring of Witt vectors over such a field.