I've been on a heraldry kick for the last 36 hours or so. Decided to mock up a House Mires Shield from Winter of Widows by @laughingnell . And then I decided to make a joint shield for Bill and Ursula because thats what people did in the Midieval era. Three versions.
We have a quartered shield, where each insignia is represented in a checkered like pattern. We have a split shield, where you theoretically cut both shields in half and shove them together, but I shoved the Burley white knife over a little to be more readable (I'm sure historically there was a side for the husband and the wife, but google did not give me a quick answer, so I put House Mires on the Left as Ursula is the Lady of her house, and William is just a younger (3rd?) son, and left felt more dominant). Then we have a merged design of just throwing the white knife over the bridge (not as happy with that one.)
If I was going to do another design, I would either have a green shield with the blue triangle over it, and have the knife be red, or keep the blue and green waves and make the upside down triangle red to keep the knife white.
I don't think Ursula would change the design, because I think in the early chapters she mentions her little brother designed it, so I imagine either a split/quartered shield, or just adding in the Burley white knife would be the direction they went.
Please be kind. I'm doing this in MS Paint.