Aw, sorry you are having problems with the parents. It's worse than having problems with the kids isn't it, yeesh. I'm honest with the parents on a daily basis about their children's behaviour problems. I don't put anything in writing, it's all verbal and you have to know your audience.
Some parents are great and want to make sure their child is behaving and doing well and can see their child's faults clearly. I'm pretty sure I scare away any families at the interviews who are like the ones you describe and the only ones I have in care are the ones like I'm describing. Because from the interview stage I make sure they know that we have to work as a team consistently.