I have agreed to marry DP......

Are you thinking about naming your children ceremonies?
You could maybe reconceptualise the whole event as a family-bonding-and-celebrating event? Are you changing/double-barrelling your surnames?
The other thing that the mixed flowers people did was to decorate the venue with photos and mementoes of their lives together up until that point, in date order around the walls, which was nice - it made the journey of their time together really central. Maybe you could do that and have some way for friends/family to add in their memories of your family lives?
I've often thought about how I would do a wedding, seeing as I feel like you that a lot of it is misogynist bollocks. I think I would have to start with a blank sheet and then make a list of all the elements that I did want to introduce eg:
Family and friends come together
A big meal
Saying some vows/promises publicly to each other/speaking publicly about our mutual appreciation of each other
Music
Dancing
Children included in the ceremony in some way

How old are your children? That might affect the ideas people have for involving them?

I know a family with quite young children where all four of them walked into the ceremony together. So the guests were seated, and the family all walked in and to the front. That looked nice (wasn't actually there, saw the photos after).

Oh, and I know one couple with older children where the eldest read out a little thing he'd written on his family (you know, their traditions and funny ways, etc) which apparently had the guests in both fits of giggles and misting up.

We went to a "wedding" recently which took place after the official ceremony & was in the form of a mini play performance. The "celebrant" was the narrator & told a sort of embellished version of the story of the couple's lives & how they met etc Some members of the audience had bits as well. It worked quite well & they are of theatrical/arts background so suited them down to the ground. It was the most unique ceremony I've been to & was very memorable - I'd never do anything like it in a million years myself but just mentioning for possible inspiration.

Just go away on a holliday, just the two of you, maybe an adventure-holliday.
We went to Svalbard and got married, just us two, spent a couple of days hiking and got married at the Sysselmann's office, then celebrated with an outragesly expensive, but best meal I've ever had at the local Radisson. The whole trip was magical and it all felt so real and deeply personal because it was just us two together at this remote place. I guess I'm not much of a ceremony kind of girl :-) Later we took friends and family out for a nice meal in a restaurant to celebrate with them.

I went to a wedding once which was the second marriage of both parties, and the adult children of each of the couple came in with different flowers (ie bride's children had daffodils, groom's children had tulips), and there was a point in the ceremony where they exchanged flowers to make mixed bouquets. That was simple but has stuck with me. Yours isn't a blended family but maybe a way to adapt that idea?