How do you stop a 13 and six year old sibblings from fighting so much?

Start sending them both to their own room everytime no matter who caused it. Don't ask any questions, just say you don't want to listen to it. Do this even if you have to do it 100 times a day for a while. They'll get tired of it soon and lessen their fighting.

You can also tell them to settle it between themselves unless they want you to settle it, and if the bickering continues after that then come up with a solution that makes them both losers. Eventually they won't want you involved and they'll figure out a way to get along or settle their differences.

They are probably both fighting to be "right".  Don't be judge for them.   Put them both in their room.  Make them write down or think about ONE THING THEY did wrong.  NOT the OTHER PERSON.  Keep them separated until hostility is gone.  Find something ( a project, a game, an activity) that they both like and can be involved in together that is POSITIVE so to great some fun, happy memories.

Siblings without Rivalry is a good book.  See it here as well as others.  Read the reviews. http://astore.amazon.com/wwwcjkidzcom3-20?node=5&page=2

Thanks for all your help and advise i will try that all and i will check out that book that was suggested