My likes from your list in order:
Ennis - Haven't heard this in ages but I do like it. NEVER would have thought of EEnnis pronunciation. Really nice with Willa!
Henry - Willa and Henry sound good together. And Henry is a classic.
Lewis - Like the name better with the spelling Louis. I think its due for a revival!
I do love the name Charles but don't know any Charles nicknames I like. I do like Charles and Willa together though.
I can't actually imagine problems with Ennis. If you love it, use it.
Otherwise, my favorite from your list is Louis (spelled that way, not Lewis). Willa and Louis--both nice strong classic Germanic names.
Thank you all so much for your replies! It's so helpful to hear your thoughts. I agree that the Willa/Henry combo is compelling! I'm glad to know most of you didn't go to a bad place with Ennis!
I wouldn't do Ennis. I do love Henry and I adore Nicholas. Nico as a nn is unique where I love, and I really, really like this option. Willa and Nico, Willa and Henry. You can't go wrong...although my heart is totally swooning for Nico!
My favorite from your list is Lewis, spelled this way (obviosly i'm in the minority there though) but I also love Charles (I've not met a young charles and I'm often around kids so I don't think this is too popular) and Walter (my gpa's name <3 )