Thanks for coming back OP. I really feel for you. This is so hard for you, because you are having to make some pretty quick decisions about how to deal with the DCs, while at the same time process your shock that what you have believed about your H is at odds with what you have now found.
Given what you've said, I think the only thing you can do is to explain to the DCs that you disagree with porn - and explain why. But don't water down your views just because they are odds with what your H thinks. I think if you feel you've got to subsume your own beliefs in order to protect your H, it will fester more.
Explain to them that you were in complete shock yesterday and remind them that shock causes people to make sometimes very bad decisions. Hence, you accused them (via your DD) before your H. Apologise for that and at the same time, praise your DD for having the strength of character to assert her own beliefs. However, acknowledge that you understand her own disappointment in her Father. Does she have any idea what those images were? In your shock and anger, did you tell her?
You could perhaps say that unfortunately, many porn users don't know the provenance of it, how it is made, the effect on the actors and their working conditions, how they came to be making money this way, or the gender politics associated with it. They just use it without thinking, often becoming ever-more de-sensitised to the images they are seeing. Explain its addictive qualities too.
You might say that you want to talk to their Dad about that, because you think that like many people, he is an "uninformed user" and you hope that he will consider the wider aspects of porn. You might also say that just like the boys at school use porn because there is a societal construction that they will, in a way their Dad is no different. That there is no societal expectation that "all women use porn" and so lots of women and girls don't have a self-expectation that they will use porn.
The conversation with your H and where you go from here in your marriage is a separate issue, in my view and is perhaps for another post.