Whingeing about the workload
Most of us are driven at times to complain about how much we have to do. Some, though, make it into a way of life, with the mantra, "I'm the only one who does anything round here" practically tattooed on their foreheads.
It's off-putting, cuts no ice with management, and is as insulting to colleagues as it is inevitably untrue.
I have seen it act as a brake on internal promotion and on external job-seeking, too, because not only does word get around, but hints of the attitude inevitably leak into the complainer's interview responses.
What is the right thing to do?
The job isn't about you. It's about the school and the children you serve. So even if other people really are coasting at your expense, which is unlikely, public whingeing won't solve the problem. Button up, do your own job well and let that speak for you.