Oh you poor things!
I've only dd and she's past this stage but I used to be a childminder and I'm eldest of 3 myself so I definitely have some experience of this.
My mums the eldest of 6 and was often left "in charge" during school holidays (no childcare then and parents both worked 2 jobs each!)
And one of her siblings is definitely "can cause trouble in an empty box" type - STILL like that now, the other siblings don't tell them anything secret or surprise related etc as they'll still mention it to the worst person possible! And they're in their 60's and 70's now! It's actually quite amusing from an outsiders perspective when they end up STILL arguing over who stole who's dolls pram in 1959 and why he dropped me in it with dad about that boy I was seeing dad disapproved of - they totally revert to kids! 
Her mum did once kinda lose the plot and "tied" them all together with a skipping rope at the waist on one occasion very briefly until they could co-operate (similar idea to pic)
My mum always said (wondering if scottishbadgers mum is also scots?)
As long as nobody's bleeding or dying I'm not interested! Sort it among yourselves!
Bro still comments (we're all in our 40's now) how he usually stayed well out of it if I was fighting with my sister "cos girls get VICIOUS when they fight! Boys throw punches and kick, girls bite, scratch, pull hair, clothes, use weapons!"
He was less likely to fight physically with us but was a pita for "niggling" shit - poking in arms or legs, nipping, whiny voiced "impersonations" repeating things we'd said, hiding toys etc - git 
We were lovely to him 😇
Hmm ok maybe not...we may have niggled him too and ganged up on him once too often 😈