Oh my goodness!!You really do have a problem. The issues all need to be addressed, you are absolutley right, but I don't think you are going to get very far with the school. Sounds like it should be on special measures rather than middle of the rd.
To speak to the school is brave and right for you and your children and moralistically what I would do. And its your 1st point of call.
But...you may end up taking some flak from the school.
Worse case scenario If a chat with the ht doesn't work contact the LEA.
Ultimatley if you do nothing, nothing will improve.
Whats the PTA / friends association like?
There is usually one v dominant female in the pta or whatever who is good at getting changes happening - You might have some support from that area.
good luck!!