Praise your children when they are polite and considerate. It was kind of you to help your sister put her toys away. She was very happy. If you express your feelings and solve problems by talking rather than yelling, your message will be that much stronger. Your children will learn from watching you and listening to you.
Conflicts are often more common when children are tired, bored or have spent too much time together.
Providing quiet time, or private spaces where children can safely be by themselves, may help prevent conflicts. You do not have to treat children the same to be fair. Children have different needs and different personalities. For example, it's fair to allow older children to stay up later. It's fair to give younger children some extra attention when they're tired.