Thank you so much for the compliment on my Natalie's name! It was so sweet of you! Also, Liora Ophelia would have to be my favorite of the girls' names! Liora is so pretty and uncommon, which something that I adore in names (although my daughters have fairly common ones)! Liora is easy to pronounce, and it could honestly be perfect for any age. I truly cannot get enough of it! I love all of your options! Your little baby will definitely have a beautiful name, regardless of gender! Also, suggestions, I think your combinations currently are perfect, so I won't suggest new firsts or middles. I do have a few ideas. I am not the best at this, but here goes:
Douglas- I just think that Douglas has a royal feel, like Edmund, Hugo, Jasper, and Caspian do to me. Doug is honestly not the most appealing nickname, but I think the full name - Douglas - may be your style? FYI, it means "black stream".
Arthur- I also think that Arthur is royal-sounding(?) and I think it goes well with your other boys' options. This one means "noble, courageous".
Douglas Arthur or Arthur Douglas would be quite the combination. I think they go well together, but the full name may be a bit formal.
More first and middle name combos for these...
Douglas Leo
Douglas Henry
Douglas Jacob
Douglas Frederick
Douglas George
Douglas Timothy
Douglas Jack
Arthur Leo
Arthur Henry
Arthur Jacob
Arthur Frederick
Arthur George
Arthur Timothy
Arthur Jack
Mabel- I feel that this fits in with your other girls' names. It doesn't have that "spark" that your other girls' names have, though.
Willa- I think that this sounds like the type of name that you like. I don't have much else to say, otherwise.
Willa Mabel is nice. I think it is much more "expected" (if you will) than your other girls'names.
More first and middle name combos for these...
Mabel Celeste
Mabel Anastasia
Mabel Elliora
Mabel Calidora
Mabel Adeline/a
Mabel Apollonia
Willa Celeste
Willa Anastasia
Willa Elliora
Willa Calidora
Willa Adeline/a
Willa Apollonia
Good luck! Sorry if these are poor suggestions
~ Mal