Middle names starting with X?

We just found out were having twins and my husband is a huge dork. My name is Quinn Rebecca and his is Sebastian Tyler (Q R S T) so when we had our first, we named her Ursa Veronica to fit the pattern. It was kinda a joke honestly because we just both really liked the name Ursa but now that we're having twins, he's insisting that their initials be W.X and Y.Z.

I don't necessarily have an issue with it, though I do think its a little silly, but we can't think of any X names we like. We have ideas for Y.Z but are just stuck with this X name. We don't know the genders yet but for a girl we like Willow and Winter and for a boy we like Westley and Wren, so any X names that go with those would be great. Any ideas?

Edit: Husband stresses that we cant go with M.N and O.P because it doesn't fit the pattern. It goes by age. I'm a month older than my husband and obviously our daughter is younger than us and older than the twins. It would end up being Q R S T U V M N O P. Which defeats the point.