Constant bickering, how to deal with it?

[Olivo]

I feel like a full time referee between my two DDs age 8 and 11 and it is exhausting.

Can anyone give me any tips on how to deal with it?

I do this as my day job between teenagers, but I am stumped when it comes to my own

This might be a rubbish idea but what about rewarding them for solving problems together? Every time they manage to solve an argument calmly without involving you, they can earn points towards a treat e.g sweets, swimming, pocket money,

I had 5DDs, so some pretty hair raising bickering at times! If it all got too much I used to quietly say "O.K. I've had enough of all this nonsense now so I'm not being mummy for now and I'm going to my room." I would then take myself upstairs and close my bedroom door. Worked every time.
Don't forget though that they are learning some pretty good negotiating skills for real life by their arguing. All fine as long as it doesn't get physical and the younger one can hold her own.Good luck OP if it's any consolation they do grow out of it eventually!