8.Martha - a bit dull and dowdy for me
3.Eva -classic, simple and very international
1.Lydia - elegant, classic and underused
4.Clara - lovely but a bit trendy now (prefer Lara or Cara)
2.Ada - (Lovelace - cool namesake) one of the few "old-lady" names I like as it has a nice sound
5.Grace - nice but a bit overused for me
6.Olivia/Olive - Olivia is lovely (classic and Shakespearean) although very popular, but Olive is more geek/hipster chic and not my taste
7.Demelza - too Poldark, but a fun middle name (especially for a simple, popular name like Grace)
Since many of your first name choices end in "a", I'd look at other endings for middles - like Sophie, Alice, Charlotte, Erin, Xanthe, Iris, Rosalind, Elizabeth, Isabel, Catherine, Juliet, Josephine, Madeleine, Faye, Esme, Sylvie, Eve, Tess, Lily etc, depending on how many syllables your first name choice and surname are.