I am not sure if you have come back to your thread or not but here is my advice...
Re So do we just say that we can't get child care and so DH and I can't go?Yes, if you really do not want to go anyway.
Re Do I go on my own and spend the day feeling like s@&t. No, I would not do that, if you can't go and enjoy it then don't bother.
Re Or do I go down the emotional blackmail route about how DN is allowed but mine aren't.. I wouldn't personally do that but I would say how much I would like to bring my kids and I would offer to pay for them, if you feel that is appropriate to do.
Re ...how horrible it would be for it to stop being a family veil because my DD won't get to see it and I wish that I had never worn the veil in the 1st place? This is a total overreaction. The veil is a family heirloom and will continue to be so whether your dd sees it on someone else. (Bear in mind she may not wish to wear it one day anyway, some people don;t like to follow tradition.) if you wore it it was special to you and your dd may appreciate it.
I really think you need to chill out about this and not worry too much.
At the end of the day a wedding is to celebrate the happy couple in the way they would like to celebrate. It is not about providing a nice time for your kids, who may not enjoy the wedding anyway. My dd has autistic tendencies and I am not sure she is mad keen on weddings.