I've been weighing your specific suggestions and your gentle nudges in the direction of using a MN w/ meaning.
I think the MN will be Ellison. The literal translation, Ellie's son, honors William, my DH. And the name itself honors Ellie, my dear MIL. I'm hoping all of this won't be very clear to my mother. If she questions the name, I may resort to a white lie and tell her simply that I think it is great name, end of story. Don't know that she'll believe me, though.
Daphne Ellison???? If so, I need to start selling William.
Oh, and two last doubts: 1. Would you consider having two children w/ "ee" last syllables repetitive?, and 2. Is Ellison too masculine? (Please, anyone else reading this message, feel free to offer input.)