I have real sympathy with you on this one. My mum's 86 and has 6 of us. The family used to get on great...we didn't all like each other enormously, but we kept everthing in check. Then dad died...and mum was poorly...and the bitching began with avengance.
One of my sisters wanted to put my mum in a home cos she got flu one Christmas (long story...I won't bore anyone) so the family split in two. My mum knows there's been trouble and she knows we don't all get on, but we try to keep it to ourselves.
I'd love her to know things from my perspective, but at the end of the day, I know she would never believe my version of things. I was her least fave child...And to some degree it would be cruel to tell her half of what went on, so she lives in ignorance (partly from choice I suspect) and we all maintain a civil approach to each other in front of mum.
I have only one child and thought it's not out of choice, I'm glad, in retrospect, that my dd won't have that to contend with. On the other hand, I'd give anything for her to have brothers or sisters to share stuff with. Even the bad stuff.
Just tell your kids they're lucky to have each other. And you don't want to get involved in all their fights and niggles.