This.
Of course it's deliberate.
Its a sport to them.
I feel so sorry for your 10 year old, that you inflicted this disney waster on her and then had another child.
They have no respect for you and they certainly don't for him.
How well he found a woman to skivvy for his children🙄.
Look at separation, it is not in your poor childrens best interests to remain.
That waster is never going to stand up to his children.
Until such time as you get split up, stop doing ANYTHING for his children.
Stop cooking, shopping, laundry.
Stop everything.
Personally I would packing up their filth, the sanitary towels with their clothes and sending them and their filth home to their mother.
I would also photograph the state of the loos and send it to their mother and father and ensure he cleans up.
Actually you could start photographing their filth and ask them would they like the school to be informed as they obviously need support.
Can you cease sharing facilities with them?
Do you work?
Are you paying for them?
If so, stop.
OP, you are a part of the problem.
Start acting smart and start protecting your 10 year old who is stuck in the middle of this filthy shit show.
They are only laughing at you.