The word "himself" is a reflexive pronoun that refers back to Satan, and it is also a metonym for his evil spirits. Alternate translation: "If Satan and his evil spirits were fighting one another" or "If Satan and his evil spirits have risen up against each other and are divided" (See: [[rc://en/ta/man/jit/figs-rpronouns]] and [[rc://en/ta/man/jit/figs-metonymy]])
Here "stand" is a metaphor that means endure, or stay strong. Alternate translation: "cannot endure" or "cannot stay strong" (See: [[rc://en/ta/man/jit/figs-metaphor]])