We got married! It was wonderful, the DSC were with us and the four of us have never felt closer or been happier. They were on terrific form, we were so proud of them and I can't imagine not having had them there. They did all the jobs they wanted to - handing over the rings, confetti distribution (!), being in photos. It was a low key do but turned out quite a bit more weddingy than we'd intended due to their involvement, which was so lovely.
We had a heart stopping moment when we went to pick them up on the way to the wedding and there didn't seem to be anyone home and their DM wasn't picking up. Suddenly seemed to have been an awful mistake to have told them when it was happening and give her a chance to scupper it!
But we were wrong to worry (and I felt bad for thinking she'd do that), the DSC eventually came tumbling out very excited about it and we had a brilliant couple of days. And, while I worried about it for months, my now DH was right to give the DC a chance to enjoy the build up and preparations as we got to. They kept referring to it as "our wedding" i.e. all of us, and that was more than we'd have hoped for and a testament to my DHs way of talking to them about it all I think. He's been wonderful.
Their DM knew it was happening but said not a word to my DH at pick up or drop off that weekend and I doubt it'll ever be mentioned between them. The way they (don't) communicate is a mystery to me, but seems to keep drama to a minimum.
So thank you to everyone who gave advice and shared your own stories, fascinating what a variety of situations there are, but that's families and step ones perhaps particularly.
When I look back on the day - saying my vows with a sticky little boy hand squeezing mine, endless stops for trips to the loo, seeing how happy they were at the whole thing, loving my DH for what a good father he is and how much that means to me - it's not something I could ever have imagined but it is something that makes me happy. I doubt we're out of the woods, but so far, I'm grateful for what we have.