Give each child individual attention. Spend a few minutes daily with each child, say 10 to 15 minutes. Periodically have a special activity doing something with each child separately. Giving your children individual time and attention reassures them that their place is secure with you. Equal treatment is not as important as meeting unique needs.
Description is better than comparison.
Expecting them to play together or get along all the time will only drive you and them crazy. Also, give each child some physical space that he can call his own. If two brothers share the same room, make some definitive division of space. This might be done in the placement of the furniture. Make sure that each child knows his territory.