I very much doubt this man has emotional intelligence of the kind that serves the needs of others.
My take on him is that he likes to be treated as if he is some sort of oracle, looked up to, seen as wise, giving, generous with his time, and yes 'emotionally intelligent', etc.
He probably is a very good reader of other people. Narcissists tend to be.
They read other people well so that they can fine tune their attack strategy. Everything in their interactions with other people is designed to feed their bottomless pit of ego need. They will find the buttons to press and they will press them. In the case of your DH, you are wrong to think he is 'clueless about inappropriate behaviour'. This is all calculated. He has found the button to use against your DD, and no doubt he knows what button to use against your DS too. His emotional intelligence is used in the service of evil. I don't use the word evil lightly.
But there's something about him that either refuses to, or is unable to, acknowledge the feelings of children. It's as if he regards them as an extension of him, rather than individuals in their own right.
Bingo.
To acknowledge their rights would be to see his entire conception of himself crumble into small pieces at his feet.
What he has been getting from family life, from fatherhood, is the feeling that he can do as he pleases, that nobody matters except him, that he is a sort of godlike figure among the adoring lilliputians if you will.
Naturally, when children are small they don't notice their rights being trampled. What they experience is all they are used to - they have nothing to compare their lives to, no prior life in a family other than their own. They don't notice that they are being used to provide reflected glory (golden child) or to be the repository of everything a narcissist parent rejects in him or herself (the scapegoat or black sheep). They don't notice the games their narcissist parent is playing.
As they get to their teens they develop a concept of themselves as individuals - a healthy and normal growth of the personality - and suddenly the narcissist parent has no satellites in orbit around him. Their normal development in intellect, emotional and social fronts is an affront to him. It is experienced as a deep insult that these beings (whom he now considers worthless, in a cycle of pedestal to dustbin/devaluation) are letting him know that they are separate beings. The children are now seen by him as adversaries. As NotYoda remarked, they will stoop as low as fighting bitterly with their own children.
It's just become more apparent as the kids have got older and he has failed to adjust his parenting approach to their developing needs.
Please don't discount the element of nakedness or partial undress in this. That part may not be overtly sexual. It may not indicate the desire to molest his daughter.
BUT - it indicates a desire to demonstrate to himself and to her that he can be powerful in a situation that he in entirely in control of, a situation where the other person is caught on the back foot, vulnerable and surprised because of various possible factors associated with the scene that he has engineered (DD could be naked, half naked, checking out her breasts or examining her vulva. Or she could just be doing her nails or brushing her hair or reading a book, whatever) whereas he is fully clothed, not surprised, and in control.
The points he is trying to make to DD are:
(1) He is powerful and she is vulnerable, weak, at his mercy;
(2) She must always have him front and centre in her mind. If she won't give him that impression in her teenage demeanour that she may have inadvertently given him as a child then he is going to see to it that she is forced to remember that she is his satellite because he will intrude on her and make sure she always keeps an ear peeled for his footsteps, and she can't ever block out his presence. Or he will exact revenge for 'turning on him' as he sees it. Either way, he knows what button to press for the effect he wants to achieve.
Your DH has built an emotional fortress around himself consisting of outrageous, aggressive, unreasonable refusal to listen to anyone's objections to his behaviour, and fierce insistence on his 'rights'. Every transgression of the boundaries of others is another brick in his fortress, another reaffirmation to himself of how great he is. What he is saying to himself in all of this is extremely important.
To surrender (i.e. to agree that he is wrong and that others have rights and that he must listen to others and change) would therefore be unthinkable. It would be worth more than his life.
A lock would just cause more problems. I can see him demanding to be let in if it is locked which would escalate tensions further.
You are right to predict this.
This is what narcissists do when they sense resistance. He will not confine his defence to demands to be let in though. He will find other avenues of attack, and there will be lots of rage.
There is no parenting course that will cure this.