One of the best, if not the best, parenting tool there is would be having entrenched a fixed set of universally consistent set of GROUND RULES. You know ... rules like “Do not do unto others....” You can devise your own that could resemble the one below:
a. Love one another at all times
b. Keep your room neat and tidy
c. Clean up and return things to where they’re kept after using
d. NO FIGHTING, no biting, no spitting, no cursing
e. Respect the property of others, etc.
You can formulate these rules with your children. Have them chip in, let them own these rules. When they feel empowered, when they feel they own the rules, it would be easier for them to stick to these. You can discuss and explain these with them, have them printed and posted on the fridge where everyone can see them. It doesn’t matter if some kids can’t read yet --- they would pretend they can because they must already know these by heart.