The difficulty with this now is that in trying to clear up this mess for your H, you seem to be normalising porn use to your DCs, so that they don't view their Dad as a perverted monster. If prior to today, you had only spoken to your DD about porn and have strong political views about it (which I share incidentally) then she has followed your good parental steer and is now being punished for having very strong anti-porn views. She must be very confused indeed about where you stand on this issue.
What did you say to your DS, out of interest? I hope you didn't tell him that porn use was okay?
I find it odd that you can have done so well with your DD and yet your H seemed completely unaware of your strong views. Or is it the case that he did know, but disregarded your feelings about it?
In your shoes, I would stop trying to cover up for their Dad and make your views really clear to the DCs, because at the moment I think you might be coming across as hypocritical.
Your daughter is presumably old enough to hear that you are deeply upset about her Dad's actions and that this is something you're going to need to resolve with him. It's okay to tell her that he has shocked and disappointed you, but that you think that it's something you can sort out.
Your DD has a right to be angry with both of you right now and some of this is because she has suddenly lost a lot of respect for her Dad. When this has calmed down, assuming he is going to give her the right messages about porn and not trivialise it, he should be speaking to her about it and telling her that he was wrong.
Your secondary issue is how you deal with the fact that your H uses porn and is effectively telling you to get over yourself, as it's normal. Only you can decide where you stand on that. It's his right to continue using it, just as it's your right to say that you won't put up with it. He then makes his choice, doesn't he? - porn or you.
Having read your most recent posts, I agree that he was trying to leave you a message, but that is based on what seems to be rather smoke and mirrors communication in your marriage.