Agressive cats

Question
I have 2 (7 year old) cats that are brothers.
Within the last two weeks, they have started fighting with each other and staring each other down.  We have had them since they were kittens and were raised together. Which is why I do not understand this recent agression problem.  They can eat breakfast and dinner together and then go and groom each other for a short time and then 30 minutes later you see them hissing and growling and ready to rip each other apart.

any help would be greatly appreciated, It is making a very stressful household.

Answer
all they are doing is fighting to be the top of the household. We have seven cats and one of the cats is like the leader of the others cats and always starts fights with all them. Theres nothing really you can do but if you see them seriously fighting then just get on to them.