Sibling Rivalry older children - is it too late to change situation?

[mollyroger]

Sorry, posted this in chat originally.
my boys are 11 and 8. We really really do try and keep things fair, and mostly they rub along nicely.
But at the minute arguments and fisticuffs are breaking out every hour it seems. I am losing my laissez faire and have resorted to shouting in a John Cleese stylee.
Is some of it the 11-year-olds' natural pre-teen stroppiness kicking in? (it's a very anxious time for him)

But how can I get them to supprt each other instead of killing each other?

Me and my sister hated each other at that age too. SOrry, no suggestions.

agggh! So do I just have to grin and bear it? Do you and your sister like each other now?

Yeah, we are really close now and spend loads of time together I think we just had to get it out of our systems.