This can be stated in active form. Alternate translation: "This is how we know who the children of God are and who the children of the devil are" (See: [[rc://en/ta/man/translate/figs-activepassive]])
"whoever does not do what is righteous is not from God; whoever does not love his brother is also not from God" or "those who are from God do what is right, and those who are from God love their brothers"